Hard Math Riddles for Adults Who Love Numbers

I am a three-digit number. The sum of my digits is 12. My tens digit is twice my hundreds digit. My ones digit is the tens digit minus two. What number am I?

I am a three-digit number. Reverse my digits and subtract the smaller from the larger to get 297. What number am I?

Three consecutive integers add up to 177. What are they?

A shopkeeper buys an item for $60 and sells it for $70. Then he buys it back for $80 and sells it again for $90. How much profit did he make?

If 8 workers take 10 days to build a wall, how many days would 10 workers take, assuming equal efficiency?

If 3x + 5 = 26, what is 6x + 10?

A sequence goes 2, 4, 7, 11, 16. What is the next term?

The product of three consecutive integers is 990. What are they?

If the perimeter of a rectangle is 50 and the length is 15, what is the width?

I am a two-digit prime number. The sum of my digits is 10. When you reverse me, you get another prime. What number am I?

A train travels 60 mph for 2 hours and 40 mph for 3 hours. What is the average speed for the entire trip?

What is the smallest positive number divisible by both 12 and 15?

If 5 cats can catch 5 mice in 5 minutes, how many cats are needed to catch 100 mice in 100 minutes?

I am a number that is the square of a prime and also the sum of two consecutive primes. What number am I?

If 2^x = 128, what is 2^(x+1)?