Cooper2248817
Does any body know about divisibity rules?
2 if the last digit is even
3 if the sum of all digits is divisible by 3
4 if the last 2 digits of the number is divisible by 4
5 if the number ends with 0 or 5
6 if the number is divisible by both 2 and 3
7 double the last digit and substract it from the rest of the number
Eg: 1113, double 3 which is equal to 6 and substract 6 from 111 = 105, which is divisible by 7.
8 if the number formed from the last 3 digits is divisible by 8, then the original number is divisible by 8.
9 if the sum of digits of the number is divisible by 9, (similar to divisibility rule for 3)
10 if the number ends with 0.
11 Compute the sums of digits in the odd places and even places separately and substract the sums to compute the result. If the result is divisible by 11, so is the original number.
Eg: 1221 (1+2)-(2+1) =0 which is divisible by 11.
Please post if there are simpler means of testing divisibility.
And I don't think that a simpler method exists to test a whether a number is prime or not. GMAT questions related to prime number just appear to focus on the starting prime numbers.