Trick questions

Seventeen sheep, and a sentence that already answered you

A farmer keeps 17 sheep. All but 9 of them wander off. How many does the farmer still have?

Eight is what subtraction hands you, and it counts the sheep that left. All but nine means nine stayed behind, so the answer was sitting in the sentence before any arithmetic started. The 17 is scenery. All but nine of the sheep takes about four seconds once you have read the phrase properly.

Every question in this topic works that way. The numbers are small and honest. The trap is in the wording, and reading is the skill being tested.

Why does the sentence win?

Three mechanisms cover almost all of it.

Numbers pull attention away from words. Once digits appear, the reading stops and the calculating starts. A hole in a field is 6 feet deep and 3 feet across, and the question asks how much soil is inside it. The dimensions describe the emptiness, so the answer is none of it. The volume you can compute is the soil that was carried away when the hole was dug. The soil in a six foot hole is the shortest example on the page.

Scaling both sides at once feels safe. Six printers take 6 minutes to print 6 posters, so 30 printers and 30 posters look like 30 minutes. Each printer spends 6 minutes on one poster, and adding printers and posters in step leaves the clock exactly where it was. The answer is 6 minutes. Find the rate for one worker before you scale anything. Six printers, six posters, six minutes is that rate question in one card.

A ratio feels like a fixed property. A father is four times as old as his son, and in 20 years he will be twice as old. Ratios move as people age, and the gap between two ages never does. The son is 10 and the father is 40, so in 20 years they are 30 and 60. The fixed quantity is the 30 year gap, and every age puzzle turns on finding it. Four times as old, then twice as old is the one to try before you trust that instinct again.

How do you read a trick question?

Five instructions handle most of them.

Read the phrase before you read the numbers. All but nine. How many have 28 days. How much soil is in the hole. The verb and the qualifier decide the question, and the digits only fill it in.

Check for the word exactly. Every month runs past a 28th day, so all 12 months have 28 days. February is simply the only one that stops there, which answers a different question containing the word exactly. Months that have 28 days is a good test of whether you slowed down.

Ask what each rate is per. Six posters per six printers per six minutes is one poster per printer per six minutes. Write the per out loud and the scaling stops being confusing.

Handle the last step separately. A snail climbs a 12 metre well, up 3 metres each day and down 2 each night. Net progress is 1 metre a day, which suggests 12 days. The snail starts day 10 at 9 metres, climbs 3, reaches the top, and never slides back, because there is no night after the final climb. The answer is day 10. The snail in the twelve metre well is the classic version.

Name the unknown, then read the sentence again. A brick weighs 1 kilogram plus half a brick. Call the brick B: half of B is the missing kilogram, so the whole brick is 2 kg. Answering 1.5 treats the half as half a kilogram, and the sentence halves the brick. A brick and half a brick rewards one careful re-read.

Where people fall

Answering the complement. Eight sheep instead of nine, two cookies instead of three, the soil removed instead of the soil inside. The arithmetic is right and it describes the other half of the situation.

Multiplying a headline instead of a total. Buy one get one half off, against a flat 35 percent off both. Half off one shirt out of two is 25 percent off the pair, so you pay 75 percent of the pair. The flat offer leaves you paying 65 percent, which is cheaper. Buy one get one half off, or 35% off is the comparison written as a single price for a single basket.

Losing track of which number a percent sits on. Take 40 plus 60 to make 100, cut 10 percent to reach 90, then add 10 percent back. The last step adds 10 percent of 90, which is 9, so the total reaches 99 and never returns to 100. Step three is the one that changed its base. Can you find the mistake in three steps asks you to name the step number.

Testing a rule against one pair instead of every pair. The list 9, 3, 1, one third goes down by a factor of 3 each time, so the next term is a ninth. Halving the third gives a sixth, which fits no earlier step in the list. Check any proposed rule against 9 to 3 and 3 to 1 before you use it. Nine, three, one, a third is the shortest sequence question here.

Same shape, different clothes

Once you have seen a few, the disguises get thin. A question about cuts and pieces is the printer question wearing a saw. A question about a discount on a discount is the percent chain wearing a price tag. A question about ages is the brick, with the unknown given a name and a birthday.

That is the useful part of practicing these. The answer to any single one is worth nothing on its own. The shape underneath keeps turning up in offers, in contracts, in job interviews and in the paragraph of a news story that quotes two percentages taken from different bases.

One more disguise is worth naming. A question that gives you a total and a difference is asking you to remove the gap first, and a question that gives you a rate is asking you to reduce it to one worker, one minute or one item. Those two moves clear a surprising share of what looks like trickery.

Where these show up

Interview screens use them, because they take one minute and separate reading from calculating. Pub quizzes and group chats use them because the wrong answer is confident and shareable. Sales copy uses the same structures without meaning to, which is why the offer comparisons in this topic look exactly like the wordplay ones.

The habit that covers all of them is small. Read the question twice, decide what is being asked, and only then reach for the numbers.

Try them one at a time

The feed above holds these as cards. One question, one answer box, and a line underneath explaining where the reading goes wrong rather than repeating the sum. Nothing is timed and nothing is scored.

For longer versions with the same flavour, the blog has a set of riddles and a harder puzzle collection. If you want the version a child can play, Riddles for kids uses the same shapes with gentler numbers.