If you take away my first letter, I become a heavy weight. Take away my first two letters, and I become a fast animal. What number am I?
361
Wait, 361 is not prime (19 * 19 = 361), and 6 is even. Let's use: 253? 2 is even. Let's use 137: 1+7=8, not 3. Let's use 353: 3+3=6 (tens digit). 353 is prime! Hundreds is 3, units is 3, sum is 6, which is the tens digit.
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.
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