Burt Kaliski Jr. (@modulomathy)
4/2/12 9:45 AM
#math trivia for #April2: #93 can be checked for divisibility by 3 by adding the digits and checking the sum. Why does this test work?
The classic test for divisibility by 3 is to add the digits of a number and test if the sum is divisible for 3. This works because every power of 10 is one more than a multiple of 3. The remainder after dividing a number by 3 is therefore the same as the remainder after dividing the sum of its digits by 3. If the sum of digits is divisible by 3, then so is the original number.