A farmer looks into a pen containing only chickens and cows. She counts 20 heads and 56 feet in total. How many cows are in the pen?
8 cows
Let c be chickens and w be cows. c + w = 20, and 2c + 4w = 56. Dividing the second equation by 2 gives c + 2w = 28. Subtracting the first equation leaves w = 8 cows (and 12 chickens).
About this riddle
Math riddles hide a calculation inside a short story. Pull out the numbers, work out what is being asked, and watch for a trick such as a unit change.
Difficulty: Hard. More like this: Math riddles with answers or try Target 24 for a different kind of puzzle.
More math riddles
I am a two-digit number. If you reverse my digits, the new number is 18 greater than me. The sum of my original digits is 8. What number am I?
A container holds a colony of bacteria that doubles in size every minute. If it takes 60 minutes for the container to become completely full, at how many minutes was the container exactly half full?
I am a geometric shape with interior angles that add up to 1,080 degrees. How many sides do I have?
I am a prime number between 20 and 40. Subtract 1 from me, and the result is divisible by 6. Add 1 to me, and the result is a multiple of 8. What number am I?
Two wall clocks are synchronized at noon. One clock gains 2 minutes every hour, while the other loses 3 minutes every hour. How many hours will elapse before their displays show a difference of exactly one full hour?
Square me, and the result equals four times my value minus four. What single number am I?