I am a two-digit prime number whose tens digit is strictly less than my units digit. If you reverse my digits, I remain prime. If you add my two digits together, you get 8. What number am I?
17
Two-digit numbers whose digits sum to 8 are 17, 26, 35, 44, 53, 62, 71, and 80. The primes among these are 17, 53, and 71. Reversing 53 yields 35 (not prime). Reversing 17 yields 71 (both are prime). Since the tens digit must be less than the units digit, the answer is 17.
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: Medium. More like this: Math riddles with answers or try Target 24 for a different kind of puzzle.
More math riddles
A bag contains 3 red marbles and 2 blue marbles. Without looking, what is the minimum number of marbles you must draw to guarantee getting at least one red marble?
A lily pad doubles in size every day. If it completely covers a pond in 30 days, on which day did it cover exactly half of the pond?
Leo counts sleds in a pattern: 5, 7, 9, 11. How many sleds come next?
I start with a single bacterium. Every minute, each bacterium splits into two. If the jar is completely full in 60 minutes, at what minute was the jar exactly half full?
I bought a book and a bookmark for $11.00 total. The book cost $10.00 more than the bookmark. How much did the bookmark cost?
Spelled out in English words, which positive integer has all of its letters arranged in strict alphabetical order?