Quandaries
and Queries 

My son was asked to find divisiblity rules for 15. We have been unable to find the answer. Does it exist? Thank you, Lisa parent, 7th grader 

Lisa, I have two responses, one from Leeanne and another from Denis. Hi Lisa, There is no one single rule for divisibility by 15, but every number that is divisible by 15 must be divisible by the factors of 15, namely 3 and 5. If your son knows these divisibility rules, then for divisibility by 15, he just includes both conditions. If you are not sure of these 2 divisibilty rules, they are:
Hope this helps, Hi Lisa, , To be divisible by 15 a number has to be divisible by 3 and by 5. To be divisible by 5 the number must end in a 0 or a 5, easy enough. However divisibility by 3 is not so simple  the rule is to add up all of the digits of the number and if they are a multiple of 3 then the original number is also. For example, 9273 is a multiple of 3 because 9+2+7+3 is a multiple of 3 while 9270 is not a multiple of 3 since 9+2+7+0 is not. So, is 85721445 a multiple of 15? Yes. Denis 

