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Trap questions

Bat-and-ball questions with fresh numbers every time: the first answer that comes to mind is wrong. Catch it, then work it out.

  • Logic
  • Untimed
  • 10 levels

How it plays

Each question has an answer that jumps out and is wrong — the price that ignores the difference, the half-day that ignores doubling, the average of two speeds. The skill is noticing the jump and checking it.

The numbers and objects are new every time, so you cannot remember the answer, only the trap. Levels add kinds of trap.

Keys

Space starts and skips ahead · 1–9 pick · Enter submits · Esc stops. On a phone, tap.

What it trains

This practises checking an intuitive answer before giving it, on questions like these. It is not a test of intelligence or a cure for haste in general.

Learn

How to get better at trap questions: the method, the techniques, what each new level asks of you, and the traps the wrong answers are made of.

Your approach to each question

  1. Read the question to the end and name its family: a total and a difference, something that doubles, machines and widgets, overtaking in a race, a round trip at two speeds, or a rise and a fall back.
  2. Notice the answer that jumps out. Do not reject it yet — say it to yourself, because it is always among the options.
  3. Put that answer back into the question and test it. If the bookmark costs that much, is the difference right? If it was half full that day, is it full on the last day?
  4. When it fails, work the question through with the method for its family, and check your new answer the same way before you pick it.

Techniques and tricks

  • Take the difference off, then halve

    When two things cost a total and one costs a set amount more, the cheaper one is the total minus the difference, halved.

    e.g. ₹660 together, the book ₹560 more: (660 − 560) ÷ 2 = ₹50. Check: ₹50 + ₹610 = ₹660, and 610 − 50 = 560.

  • One day back for half

    Something that doubles every day was half the size the day before it was full. Two days before, it was a quarter.

    e.g. Full on day 41: half on day 40, not day 20.

  • Find one machine’s rate

    If k machines make k widgets in k minutes, each machine makes one widget in k minutes. Any number of machines making the same number of widgets takes the same k minutes.

    e.g. 7 machines, 7 widgets, 7 minutes: 100 machines make 100 widgets in 7 minutes.

  • You take their place

    Overtaking the runner in a place puts you in that place, and them one behind. You have not passed anyone ahead of them.

    e.g. Pass the runner in 2nd: you are 2nd.

  • Average speed by time, not by speed

    Over the same distance there and back, the average is 2 × a × b ÷ (a + b), never the plain average. If the return is twice as fast, the answer is 4/3 of the slower speed; three times as fast, 1.5 times it.

    e.g. 60 km/h there, 180 km/h back: 2 × 60 × 180 ÷ 240 = 90 km/h, not 120.

  • Falls are taken from the new price

    To undo a rise of p%, the fall is p ÷ (100 + p), because it is taken from the higher price. Know the three that come up: 20% back is 16.67%, 25% back is 20%, 50% back is 33.33%.

    e.g. ₹1,600 up 25% is ₹2,000; a 20% fall takes off ₹400 and gets back to ₹1,600.

As the levels climb

  • The families arrive in order, one every other level: the difference trap, then doubling, machines and widgets, the race, average speed, and the percentage back. Half the time you get the newest one, so expect it.
  • Between new families, the numbers grow: larger prices and gaps, later days, more machines and multiples of ten, faster speeds. The method never changes with the size; only the arithmetic gets longer.
  • Once all six families are in, it is a mix, still leaning to the newest, so naming the family in the first second matters more than speed of arithmetic.

Traps to avoid

  • The total minus the difference, unhalved: the ₹100 that makes the difference ₹460 instead of ₹560. It is exactly the first thought, and it is always offered.
  • Half the days for half the size: day 20 for a pond full on day 41. Doubling is not steady growth; the last day does half the work.
  • The number of machines as the time: 100 minutes for 100 machines. More machines with more widgets means the same time, not longer.
  • One place ahead of the runner you passed: 1st after passing 2nd. You only took their place.
  • The plain average of two speeds, or the same percentage back down. Both ignore that one part weighs more — the slow leg takes longer, and the fall is from a bigger number.

How to practise

  • Before you look at the options, say the first thought and the check in one breath: “₹100? Then the gap is ₹460 — no.” That habit is the whole game.
  • Raise “Options shown” to 6 so more answers sit around the right one and you have to compute it, not just reject the lure.
  • Leave “Time pressure” off at first. With it on you get 25 seconds a question; turn it on once the check is automatic, since hurry is what lets the first thought win.

Levels

It is untimed unless you turn the clock on. There are 10 levels with the default settings, and the counter stops at the real top. Your level is judged on your last ten answers, every ten: 90% moves you up, below 80% moves you down, which holds most people near four in five right.

All of it is in the settings beside Start — how many answers a judgement looks at and how often it recalibrates, the thresholds, the time, which questions, how many options, and whether you see each verdict at once or review them together at the judgement. You can also jump to any level.

More logic

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