1. Anagram
Rearrange the letters of LISTEN to describe a good library.
Show the answer
SILENT. Same six letters in a new order.
Lumen Lab / Brain teasers for adults that play fair
Brain teasers · 9 puzzles
Brain teasers for adults that play fair
No trick wording and no “gotcha” answers. Every teaser here can be solved with careful thinking and maybe a pencil. Answers are hidden until you open them.
2. The sale price
A lamp sells for $60 after a 25% discount. What was the original price?
Show the answer
$80. After the discount you pay 75% of the original, so 60 ÷ 0.75 = 80. Adding 25% back to $60 gives $75, which is the common mistake.
3. Painters
Three painters take three hours to paint three fences. Working at the same pace, how long do six painters take to paint six fences?
Show the answer
3 hours. Each painter does one fence in three hours. Six painters do six fences in that same three hours.
4. Counting sevens
Write every whole number from 1 to 100. How many times do you write the digit 7?
Show the answer
20. There are ten 7s in the ones place (7, 17, … 97) and ten in the tens place (70–79). The number 77 counts twice, once in each.
5. Notebook and pen
A notebook and a pen cost $5.50 together. The notebook costs $4.00 more than the pen. How much is the pen?
Show the answer
$0.75. Call the pen p. Then p + (p + 4) = 5.50, so 2p = 1.50 and p = 0.75. The quick guess of $1.50 would put the total at $7.00.
6. Half a number
Half of a number plus 7 equals the number minus 5. What is the number?
Show the answer
24. n/2 + 7 = n − 5, so n/2 = 12 and n = 24. Check: 12 + 7 = 19 = 24 − 5.
7. Letter skip
What letter comes next? Z, X, V, T, R, …
Show the answer
P. The sequence walks backward through the alphabet, skipping one letter each time.
8. Two candles
Two candles are the same height. One burns down completely in 4 hours, the other in 6 hours, each at a steady rate. You light both at once. After how many hours is one exactly twice as tall as the other?
Show the answer
3 hours. After t hours, the heights are 1 − t/4 and 1 − t/6. Set 1 − t/6 = 2(1 − t/4) and solve to get t = 3. At that point the heights are ¼ and ½.
9. A number that describes itself
Find a four-digit number where the first digit is how many 0s it contains, the second digit is how many 1s, the third is how many 2s, and the fourth is how many 3s.
Show the answer
1210, and there’s a second answer: 2020. 1210 has one 0, two 1s, one 2, and no 3s. 2020 has two 0s, no 1s, two 2s, and no 3s. Did you find both?
Why fair teasers beat trick questions
Trick questions test whether you’ve heard the joke before. Fair teasers test something you can get better at: spotting the rule, setting up the equation, and checking your answer. The Lumen Lab IQ Test is built the same way, with no wordplay traps and only original items.
Want a real challenge?
Try 24 original puzzles across logic, numbers, and visual reasoning. Taking the test is free, and the end screen shows your score range.
Start the Lumen Lab IQ TestMore puzzles: Free IQ test practiceQuick IQ testLogic puzzles with answers