Quandaries
and Queries 

how do you test a number to see if it is divisible by 7 or not? can you devise a test that works other than trial dividing? please and thank you :) 

Hi, To see if an integer n is divisible by 7, take the last digit, multiply it by 2 and subtract the result from the number formed by removing the last digit from n. This number is divisible by 7 if and only if n is divisible by 7. For example let n = 693
Since 63 is divisible by 7 so is 693. Penny 

