Honest Little AppsChallenge collections

Focus and Screen Time · 27 original mini-challenges

Deduction Choice Lab

27 original deduction questions about evidence, constraints and certainty. Nine families contain three cases each.

Choose a response. See the reasoning.

Read the facts, pick the answer that best fits the stated goal, then open the explanation. Start with five or browse the full set. There is no timer or personal assessment; the useful part is understanding the choice.

These are original web companion exercises. They are independent of the app; answers and progress do not transfer. All people and records in the scenarios are fictional. These puzzles do not measure brain age, intelligence or a health condition.

01 / reasoning

Opposite labels case 1

One token is hidden in exactly one of boxes A, B and C. Two signs read “The token is in A” and “The token is not in A.” You are told exactly one sign is true. Does that information identify the token’s box?

Show the worked answer

A. No, all three boxes remain possible

The two signs are logical opposites, so exactly one is true wherever the token sits. The truth-count information adds no restriction. All three boxes remain possible; selecting A would require another independent clue.

Try next: Add one clue that really distinguishes a box from the other two.

02 / reasoning

Follow the implication case 1

Every glow token is warm. A particular token is known not to be warm. Nothing else is stated about token categories. Which conclusion must follow from the rule, even if some other categories overlap?

Show the worked answer

B. It is not glow

If this token were glow, the rule would force it to be warm, contradicting the given observation. It therefore cannot be glow. This conclusion uses the stated implication without assuming its converse.

Try next: Explain why knowing only that a token is warm would not reverse the rule.

03 / reasoning

Pair into even totals case 1

The four number cards are 1, 3, 5, 8. Divide them into two pairs, using each card exactly once. Both pair sums must be even. Is such a pairing possible, or do the parity counts prevent it?

Show the worked answer

C. Impossible

An even pair needs two odd cards or two even cards. Here there are 3 odd cards and 1 even cards. An odd category count leaves an unmatched card, so it is impossible.

Try next: Try all three unordered ways to divide four cards into pairs.

04 / reasoning

Cycle the weekday case 1

In a calendar puzzle, today is Monday. Count forward 10 whole days, with tomorrow counted as one day later. Weekdays repeat every seven days, and no special dates matter. On which weekday does the counted interval end?

Show the worked answer

A. Thursday

10 days contain 1 complete weeks and 3 extra days. Full weeks preserve the weekday; advancing the remainder from Monday reaches Thursday. Counting today as day one would shift the result incorrectly.

Try next: Check the answer by first advancing one full week.

05 / reasoning

Four positions, fixed ends case 1

Ari, Bea, Cal and Dee occupy four positions, each used once. Ari is second, Bea is fourth, and Cal appears somewhere before Dee. Reading from position one through four, which complete order satisfies every clue?

Show the worked answer

B. Cal → Ari → Dee → Bea

The fixed clues place Ari in position 2 and Bea in 4. The remaining positions are 1 and 3. Cal must take the earlier one, leaving the later position for Dee.

Try next: Remove one fixed-position clue and see whether multiple orders become possible.

06 / reasoning

Balance-pan equality case 1

A balanced scale holds two blocks on the left and one block on the right. The left blocks weigh 4 and 7 units. You remove the 4-unit block from the left. What must be removed from the right to restore balance?

Show the worked answer

C. 4

Initially both pans weigh 11 units. Removing 4 from the left reduces that pan by 4, so removing the same amount from the right restores equality. The remaining left block does not determine the removal amount.

Try next: Write the original equality, then subtract the same value on both sides.

07 / reasoning

Inventory with one category missing case 1

A closed box contains exactly 7 tokens. Every token is red, blue or green, with no overlap between colors. There are 2 red tokens and 3 blue tokens. How many green tokens must the box contain?

Show the worked answer

A. 2

Red and blue account for 5 of the 7 tokens. The remaining 2 must be green because the categories cover the whole box without overlap. This conclusion would fail if another color were allowed.

Try next: State which assumption makes subtraction identify the missing category.

08 / reasoning

Can the rule be reversed? case 1

Every square object in a fictional collection is blue. A selected object is blue. No rule says that only square objects may be blue. Must the selected object be square?

Show the worked answer

B. No, the information is insufficient

The rule guarantees the second property for objects with the first property, but it does not exclude other objects from having that second property. The selected object may or may not be square.

Try next: Invent one collection containing a counterexample without breaking the given rule.

09 / reasoning

Exactly one filter case 1

Choose from 2, 3, 4, 5. A qualifying number satisfies exactly one condition: it is even, or it is greater than 3. Numbers satisfying both conditions are excluded. Which option lists all and only the qualifying numbers?

Show the worked answer

C. 2, 5

The qualifying numbers are 2, 5. Each makes one condition true and the other false. A number passing both is deliberately rejected because “exactly one” differs from an ordinary inclusive OR rule.

Try next: Make a two-column truth table for every candidate.

10 / reasoning

Opposite labels case 2

Exactly one token occupies box A, B or C. One sign says it is in A; another says it is not in A. Exactly one sign is true, and an independent observation proves B is empty. Which boxes remain possible?

Show the worked answer

B. A and C

The opposite signs contribute no restriction because exactly one is always true. The independent observation does exclude B. A and C remain possible, so the observation narrows the set without identifying a unique box.

Try next: Add a new observation that distinguishes the two remaining possibilities.

11 / reasoning

Follow the implication case 2

Every striped token is round. A particular token is known to be round, but nothing states that every round token is striped. With only these facts, what can be concluded about whether the selected token is striped?

Show the worked answer

C. Undetermined

Being round does not establish being striped. Both a striped round token and an unstriped round token satisfy the stated implication. The property remains undetermined because the rule does not say that its converse is true.

Try next: Construct one example for each permitted possibility.

12 / reasoning

Pair into even totals case 2

The four number cards are 2, 4, 7, 9. Divide them into two pairs, using each card exactly once. Both pair sums must be even. Is such a pairing possible, or do the parity counts prevent it?

Show the worked answer

C. Possible

An even pair needs two odd cards or two even cards. Here there are 2 odd cards and 2 even cards. Both category counts can be paired, so the task is possible.

Try next: Try all three unordered ways to divide four cards into pairs.

13 / reasoning

Cycle the weekday case 2

In a calendar puzzle, today is Thursday. Count forward 17 whole days, with tomorrow counted as one day later. Weekdays repeat every seven days, and no special dates matter. On which weekday does the counted interval end?

Show the worked answer

A. Sunday

17 days contain 2 complete weeks and 3 extra days. Full weeks preserve the weekday; advancing the remainder from Thursday reaches Sunday. Counting today as day one would shift the result incorrectly.

Try next: Check the answer by first advancing one full week.

14 / reasoning

Four positions, fixed ends case 2

Ari, Bea, Cal and Dee occupy four positions, each used once. Ari is third, Bea is first, and Cal appears somewhere before Dee. Reading from position one through four, which complete order satisfies every clue?

Show the worked answer

B. Bea → Cal → Ari → Dee

The fixed clues place Ari in position 3 and Bea in 1. The remaining positions are 2 and 4. Cal must take the earlier one, leaving the later position for Dee.

Try next: Remove one fixed-position clue and see whether multiple orders become possible.

15 / reasoning

Balance-pan equality case 2

A balanced scale holds two blocks on the left and one block on the right. The left blocks weigh 3 and 8 units. You remove the 3-unit block from the left. What must be removed from the right to restore balance?

Show the worked answer

C. 3

Initially both pans weigh 11 units. Removing 3 from the left reduces that pan by 3, so removing the same amount from the right restores equality. The remaining left block does not determine the removal amount.

Try next: Write the original equality, then subtract the same value on both sides.

16 / reasoning

Inventory with one category missing case 2

A closed box contains exactly 10 tokens. Every token is red, blue or green, with no overlap between colors. There are 4 red tokens and 2 blue tokens. How many green tokens must the box contain?

Show the worked answer

A. 4

Red and blue account for 6 of the 10 tokens. The remaining 4 must be green because the categories cover the whole box without overlap. This conclusion would fail if another color were allowed.

Try next: State which assumption makes subtraction identify the missing category.

17 / reasoning

Can the rule be reversed? case 2

Every wooden object in a collection is small, and every small object in that collection is wooden. A selected object is small. These two rules have no exceptions. Must the selected object be wooden under the stated information?

Show the worked answer

A. Must be true

The second rule explicitly states that every small object is wooden. It applies directly to the selected small object, so the answer is definite. Unlike a one-way implication, the supplied pair includes the reverse direction.

Try next: Identify the exact rule needed without relying on the other one.

18 / reasoning

Exactly one filter case 2

Choose from 4, 5, 6, 7. A qualifying number satisfies exactly one condition: it is even, or it is greater than 5. Numbers satisfying both conditions are excluded. Which option lists all and only the qualifying numbers?

Show the worked answer

C. 4, 7

The qualifying numbers are 4, 7. Each makes one condition true and the other false. A number passing both is deliberately rejected because “exactly one” differs from an ordinary inclusive OR rule.

Try next: Make a two-column truth table for every candidate.

19 / reasoning

Opposite labels case 3

A token occupies exactly one of A, B and C. Two signs say “the token is in A” and “the token is not in A.” A narrator claims both signs are true simultaneously. Is any placement consistent with that claim?

Show the worked answer

C. No consistent placement

The signs are exact logical opposites. For every possible placement, one is true and one is false; they cannot both be true. Therefore no token placement satisfies the narrator’s simultaneous-truth claim under the stated rules.

Try next: Test each box and record the truth value of both signs.

20 / reasoning

Follow the implication case 3

Every metal token is heavy. The selected token is explicitly known to be metal. No exceptions to the rule are allowed, and no other category information is given. What can be concluded about whether the selected token is heavy?

Show the worked answer

A. Must be true

The rule applies directly because the selected token is metal. It must therefore be heavy. This uses the implication in its stated direction, requiring neither a converse assumption nor information about tokens outside the metal category.

Try next: Explain why unrelated token categories do not affect this deduction.

21 / reasoning

Pair into even totals case 3

The four number cards are 6, 8, 10, 11. Divide them into two pairs, using each card exactly once. Both pair sums must be even. Is such a pairing possible, or do the parity counts prevent it?

Show the worked answer

C. Impossible

An even pair needs two odd cards or two even cards. Here there are 1 odd cards and 3 even cards. An odd category count leaves an unmatched card, so it is impossible.

Try next: Try all three unordered ways to divide four cards into pairs.

22 / reasoning

Cycle the weekday case 3

In a calendar puzzle, today is Saturday. Count forward 23 whole days, with tomorrow counted as one day later. Weekdays repeat every seven days, and no special dates matter. On which weekday does the counted interval end?

Show the worked answer

A. Monday

23 days contain 3 complete weeks and 2 extra days. Full weeks preserve the weekday; advancing the remainder from Saturday reaches Monday. Counting today as day one would shift the result incorrectly.

Try next: Check the answer by first advancing one full week.

23 / reasoning

Four positions, fixed ends case 3

Ari, Bea, Cal and Dee occupy four positions, each used once. Ari is fourth, Bea is second, and Cal appears somewhere before Dee. Reading from position one through four, which complete order satisfies every clue?

Show the worked answer

B. Cal → Bea → Dee → Ari

The fixed clues place Ari in position 4 and Bea in 2. The remaining positions are 1 and 3. Cal must take the earlier one, leaving the later position for Dee.

Try next: Remove one fixed-position clue and see whether multiple orders become possible.

24 / reasoning

Balance-pan equality case 3

A balanced scale holds two blocks on the left and one block on the right. The left blocks weigh 5 and 9 units. You remove the 5-unit block from the left. What must be removed from the right to restore balance?

Show the worked answer

C. 5

Initially both pans weigh 14 units. Removing 5 from the left reduces that pan by 5, so removing the same amount from the right restores equality. The remaining left block does not determine the removal amount.

Try next: Write the original equality, then subtract the same value on both sides.

25 / reasoning

Inventory with one category missing case 3

A closed box contains exactly 13 tokens. Every token is red, blue or green, with no overlap between colors. There are 5 red tokens and 4 blue tokens. How many green tokens must the box contain?

Show the worked answer

A. 4

Red and blue account for 9 of the 13 tokens. The remaining 4 must be green because the categories cover the whole box without overlap. This conclusion would fail if another color were allowed.

Try next: State which assumption makes subtraction identify the missing category.

26 / reasoning

Can the rule be reversed? case 3

Every striped object is soft. A selected object is explicitly not striped, and no rule describes unstriped objects. Could its softness be established from these facts alone? Treat “soft” as a simple property with no other assumptions.

Show the worked answer

C. Undetermined

The selected object lies outside the category governed by the rule. An unstriped object could be soft or not soft without violating the implication. Negating the first property does not establish the opposite of the second property.

Try next: Give two permitted examples with different softness outcomes.

27 / reasoning

Exactly one filter case 3

Choose from 6, 7, 8, 9. A qualifying number satisfies exactly one condition: it is even, or it is greater than 7. Numbers satisfying both conditions are excluded. Which option lists all and only the qualifying numbers?

Show the worked answer

C. 6, 9

The qualifying numbers are 6, 9. Each makes one condition true and the other false. A number passing both is deliberately rejected because “exactly one” differs from an ordinary inclusive OR rule.

Try next: Make a two-column truth table for every candidate.