Name: pat walsh
Question: Suppose that we have a number such as 834 567 and wonder if it is a multiple of 3.
Now we know that 3 divides 9 so if we ask whether 3 divides 834 567 or not we can reduce our problem as to whether or not 3 divides (8 + 3 + 4 + 5 + 6 + 7), i.e. does 3 divide the sum of the digits of the original number? You can see that "3" in the argument above could be replaced by "9" so that an integer is divisible by 9 precisely if the sum of its digits is divisible by 9. Cheers,Penny
