Worked explanations
deductive-reasoning-s01-q01
A statement about every member of a group applies to each individual member. Membership in the group plus the universal rule settles the case immediately.
deductive-reasoning-s01-q02
Two universal statements link end to end: everything in the first group belongs to the second, and everything in the second has the sticker. Follow the chain in the direction it is stated.
deductive-reasoning-s01-q03
The statement says where the top-shelf novels sit in the wider category of hardbacks, not that the category holds nothing else. Reversing a universal statement like this is the classic converse error.
deductive-reasoning-s01-q04
Two groups sharing a feature need not overlap each other. A shared middle term establishes no direct link between the groups on either side of it.
deductive-reasoning-s01-q05
The second statement tells you that tray 4 holds packet R seeds and nothing else, so the universal claim about packet R covers every seed in the tray.
deductive-reasoning-s01-q06
If every member of a group has a feature, then anything lacking that feature cannot be a member. This backwards form of a universal statement is always available to you.
deductive-reasoning-s01-q07
A recipe in both chapters would have to use butter and not use butter at once. Since that is impossible, the two chapters can share no recipe.
deductive-reasoning-s01-q08
A universal rule only reaches an individual once that individual is placed inside the group. The missing statement is the one that puts Ivo in the group the rule describes.
deductive-reasoning-s01-q09
"All" distributes across every member of the group without exception, so the count simply tells you how many individual cases the rule covers.
deductive-reasoning-s01-q10
The chain runs one way: quartet membership leads to a stringed instrument, which leads to a locker. Arriving at the end of a chain never lets you travel back up it.
deductive-reasoning-s02-q01
A "no" statement excludes a feature from an entire group, so anyone who has that feature must sit outside the group.
deductive-reasoning-s02-q02
Two "some" statements about the same collection may describe the very same boxes or entirely separate ones. Neither overlap nor separation can be established from them alone.
deductive-reasoning-s02-q03
Denying a universal claim needs only a single exception. "Not all" is therefore much weaker than "none", and says nothing about how many chairs stack.
deductive-reasoning-s02-q04
The collection definitely contains nocturnal animals, and no reptile there is nocturnal, so those particular animals must fall outside the reptile group.
deductive-reasoning-s02-q05
The first-aid trained volunteers definitely exist, and the second statement rules every first-aid trained person out of the night shift, so those volunteers are excluded from it too.
deductive-reasoning-s02-q06
The airport vans sit wholly inside the fleet, so an exclusion that applies to the whole fleet applies to them. What they do run on is never stated.
deductive-reasoning-s02-q07
A "some" statement guarantees that at least one such cheese exists, and the universal rule then applies to it. The conclusion inherits the weaker quantifier of the two.
deductive-reasoning-s02-q08
Since being unsigned and being filed never occur together, a filed form cannot be an unsigned one. Identifying the excluded combination is the whole of the work here.
deductive-reasoning-s02-q09
A universal claim and the statement that it has an exception are direct contradictories: exactly one of them holds, whichever way the shelf actually looks.
deductive-reasoning-s02-q10
The exclusion means no single item can be both a sample and for sale, so the two groups described on that table must be made up of different items.
deductive-reasoning-s03-q01
When the condition of an if-then statement is confirmed, its result follows immediately. This is the most direct use a conditional has.
deductive-reasoning-s03-q02
If the condition would guarantee the result, then the absence of the result rules the condition out. Ruling out backwards is always valid; confirming backwards is not.
deductive-reasoning-s03-q03
Take the statement as given: a rise above the threshold would have produced an alert, so no alert means no such rise. How far below the threshold it stayed is never stated.
deductive-reasoning-s03-q04
The condition is satisfied, so the stated result follows. Note also that the conditional describes a rule, not a cause running the other way.
deductive-reasoning-s03-q05
Once the conditional is granted, an absent result leaves no room for the condition to hold. Doubts about the equipment would question a premise rather than the reasoning built on it.
deductive-reasoning-s03-q06
The condition of the rule was met, so its requirement applies to her. A rule tells you what is required, not whether the requirement was actually met.
deductive-reasoning-s03-q07
The statement gives one route to the one o'clock opening, not the only route. Working backwards from a result to its stated condition is not a valid move.
deductive-reasoning-s03-q08
The rule states what a high score guarantees, not what a lower score rules out. Other routes to an interview are neither offered nor excluded.
deductive-reasoning-s03-q09
A conditional applies afresh to every occasion on which its condition holds, so two bookings produce two unlockings.
deductive-reasoning-s03-q10
No case number means no panel review, and no panel review means the claim was not late. A denial travels backwards along a chain of conditionals one link at a time.
deductive-reasoning-s04-q01
The statement names one thing that produces a pressure drop; it does not claim to name them all. Observing the result leaves the condition genuinely open.
deductive-reasoning-s04-q02
A conditional promises what happens when its condition holds and says nothing about when it fails. She might have arrived early by some other route.
deductive-reasoning-s04-q03
The premise rules out a jam without a stall, but permits a stall without a jam. Naming the other possible explanations is the quickest way to expose this pattern.
deductive-reasoning-s04-q04
Removing the condition removes only the guarantee, not the possibility. Other flowerless plants could exist without contradicting anything given.
deductive-reasoning-s04-q05
This is the one backwards move that does work: an arming would have produced the light, so a missing light rules the arming out.
deductive-reasoning-s04-q06
Only a pair that confirms the condition of a conditional delivers its result. Pairs that confirm or deny the result lead either nowhere or to the opposite conclusion.
deductive-reasoning-s04-q07
The rule obliges heavy lorries to use the bypass but does not forbid lighter ones from using it, so the route taken reveals nothing about the weight.
deductive-reasoning-s04-q08
The absent result is what does the work here: a fault would have produced drift, so steadiness excludes the fault. Naming the pattern helps you reuse it.
deductive-reasoning-s04-q09
A second route to the same result leaves the original statement intact while destroying the backwards inference. Looking for an alternative route is the standard test for this trap.
deductive-reasoning-s04-q10
To attack an inference rather than a premise, look for a case where the premise still holds but the conclusion fails: here, a punctual northern delivery.
deductive-reasoning-s05-q01
When at least one of two alternatives must hold and one is ruled out, the other is left standing.
deductive-reasoning-s05-q02
Confirming one branch of an inclusive alternative tells you nothing about the other. Only ruling a branch out is informative.
deductive-reasoning-s05-q03
"Exactly one" makes the alternatives exclusive, so confirming either branch rules the other out, which an ordinary "or" would not do.
deductive-reasoning-s05-q04
"Neither" denies both alternatives at once, so it behaves as two separate negative statements joined together.
deductive-reasoning-s05-q05
Eliminating one alternative in a statement that guarantees at least one leaves the remaining alternative established.
deductive-reasoning-s05-q06
To deny that at least one alternative holds, you must deny every alternative. Denying a single branch leaves the original claim perfectly possible.
deductive-reasoning-s05-q07
With the list of possibilities declared complete, striking off all but one leaves that one certain. This is elimination in its plainest form.
deductive-reasoning-s05-q08
Allowing both branches to hold does not weaken elimination: at least one must hold, so ruling one out establishes the other.
deductive-reasoning-s05-q09
The phrase "but not both" makes the options exclusive, so taking one closes off the other.
deductive-reasoning-s05-q10
Eliminating the first branch forces the second, which the reply count then contradicts. When elimination leads to a clash, the set of statements is inconsistent.
deductive-reasoning-s06-q01
A requirement states what you must have, not what is enough on its own. Meeting it clears one hurdle and leaves any others unmentioned.
deductive-reasoning-s06-q02
A necessary condition works powerfully in the negative direction: without it, the outcome is ruled out entirely.
deductive-reasoning-s06-q03
A guarantee is a sufficient condition: having it settles the outcome, while other routes to the same outcome remain possible.
deductive-reasoning-s06-q04
"Cannot without" is the standard wording for a requirement. It blocks entry when the card is missing but promises nothing when the card is present.
deductive-reasoning-s06-q05
When several conditions are all required, failing any one of them blocks the outcome, however many of the others are satisfied.
deductive-reasoning-s06-q06
A sufficient condition guarantees the outcome but does not monopolise it, so seeing the outcome leaves that condition open.
deductive-reasoning-s06-q07
Denying a requirement built from two parts denies at least one part, not necessarily both. Take care to keep the conclusion as weak as the evidence.
deductive-reasoning-s06-q08
"Only to" marks a requirement rather than a promise, so satisfying it merely keeps the application alive.
deductive-reasoning-s06-q09
When a condition is stated as the only requirement, it is both necessary and sufficient, so meeting it settles the outcome.
deductive-reasoning-s06-q10
Calling a condition both necessary and sufficient closes off every alternative route: admission happens exactly when the two recommendations are in place.
deductive-reasoning-s07-q01
"Only" introduces a requirement, so the action implies the badge. Reading it as a promise about all badge holders is the usual slip.
deductive-reasoning-s07-q02
An "only" statement flips into if-then form with the borrowing as the condition and the membership as the result, which is the reverse of what the surface wording suggests.
deductive-reasoning-s07-q03
"Unless" names the one stated exception, so with the exception absent the main statement holds.
deductive-reasoning-s07-q04
Read the statement as "if the pitch is not waterlogged, the match goes ahead", then deny the result: the match not going ahead forces the exception to have applied.
deductive-reasoning-s07-q05
The statement means that being forwarded implies being complete, so a completed application might still be held back for some unstated reason.
deductive-reasoning-s07-q06
When "every" comes before "an", each member of the first group gets its own instance of the second. The stronger reading, with one adult shared by all, would need different wording.
deductive-reasoning-s07-q07
The wording lets each reviewer choose a different chapter, so it supports only the per-reviewer reading and leaves whole chapters possibly unread.
deductive-reasoning-s07-q08
"Only if" states a requirement for the payment, so the payment happening means the requirement was met.
deductive-reasoning-s07-q09
"Only when" makes the volunteer a requirement, and a missing requirement rules the opening out.
deductive-reasoning-s07-q10
The first notice makes a ticket necessary and the second makes it sufficient. Lacking the ticket, it is the necessary half that decides the case.
deductive-reasoning-s08-q01
Comparisons of this kind chain together, so ahead-of relations line the three up in a single order with one runner at each end.
deductive-reasoning-s08-q02
Both comparisons point away from the same box, which fixes that box at the bottom while leaving the other two unranked against each other.
deductive-reasoning-s08-q03
Sketch the three positions on one line from the statements; the place that nothing lies south of sits at the southern end.
deductive-reasoning-s08-q04
Assemble the statements into one chain running from the shortest upwards; the person nobody is said to exceed stands at the top.
deductive-reasoning-s08-q05
"Immediately to the left" fixes exact neighbours, so the four shops fall into one fixed arrangement that can simply be read off.
deductive-reasoning-s08-q06
Each statement adds one link, and here the links join into a single unbroken chain from the highest scorer down to the lowest.
deductive-reasoning-s08-q07
Two items can be compared only when a path of statements runs between them. Here one pair has no such path, because each is linked only downwards to the thinnest folder.
deductive-reasoning-s08-q08
Fill the stack from the fixed ends inwards: the bottom two and the top two positions are all pinned down, so the one remaining parcel takes the only free place.
deductive-reasoning-s08-q09
The chain runs strictly downwards in age, so any claim that reverses the two ends contradicts it. Asking which statement must be false is the mirror of asking which must be true.
deductive-reasoning-s08-q10
The ledger's fixed place and the two left-of statements confine the atlas and diary to positions two to four; the one-book gap then leaves a single arrangement standing.
deductive-reasoning-s09-q01
Once one role is claimed by someone else, the remaining person's exclusion leaves only one role open to them.
deductive-reasoning-s09-q02
Start with the clue that fixes a position outright, then apply the exclusion; the last drink falls into the only place left for it.
deductive-reasoning-s09-q03
The two fixed desks leave only two free, and the neighbour restriction rules one of them out for Lena, which settles the other person by elimination.
deductive-reasoning-s09-q04
When one person is excluded from all but one dish, that dish is theirs, whatever the other clues say.
deductive-reasoning-s09-q05
Two subjects are assigned outright, and the double exclusion pins the third student to the one subject left for them, leaving the last subject for the remaining student.
deductive-reasoning-s09-q06
Test the days the book could take: only one leaves room for the following day's delivery, and the remaining parcel then takes Monday.
deductive-reasoning-s09-q07
Two placements for the middle pair survive the early clues, and the final exclusion knocks one of them out, fixing every flat.
deductive-reasoning-s09-q08
The adjacency clue allows only two orders, and the clue about the last slot rules one of them out.
deductive-reasoning-s09-q09
With both ends fixed, the adjacent pair can occupy the middle three places in two ways, and the restriction on the second place eliminates one of them.
deductive-reasoning-s09-q10
The April traveller cannot be the one going to Malmö, and the clue about May rules out the second possible arrangement, leaving one complete grid.
deductive-reasoning-s10-q01
Confirming the first condition triggers the first result, which is the condition of the second statement, so the chain carries you to its far end.
deductive-reasoning-s10-q02
Work backwards one link at a time: no email means no return, and no return means the form was not incomplete.
deductive-reasoning-s10-q03
Chains transmit confirmation forwards and denial backwards only. Confirming the end of a chain leaves everything earlier in it open.
deductive-reasoning-s10-q04
Validity asks only whether the conclusion would have to follow if the statements were granted. Whether those statements are actually true is a separate question about soundness.
deductive-reasoning-s10-q05
Valid reasoning can never carry you from true premises to a false conclusion, so this combination is itself proof that the reasoning is faulty.
deductive-reasoning-s10-q06
A dry floor rules out the overflow, and no overflow rules out the running tap. Denial travels the length of a chain in the reverse direction.
deductive-reasoning-s10-q07
Linked conditionals combine into a single conditional running from the first condition to the last result. Nothing about which statements actually hold can be drawn from rules alone.
deductive-reasoning-s10-q08
Each backwards step removes one more link: the unfilled car park rules out the coach, and the absent coach rules out the cancellation.
deductive-reasoning-s10-q09
Reasoning is judged by whether the conclusion is forced, not by whether it happens to be correct. A lucky hit leaves the backwards step just as invalid as before.
deductive-reasoning-s10-q10
Starting from the unsigned log sheet, each rule is denied in turn back along the chain, and the last denial reaches the kiln at its head.