SOLUTION: Is this closed under addition? {7,14,21,28,...} Margarita

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Question 380925: Is this closed under addition?
{7,14,21,28,...}

Margarita
Answer by jim_thompson5910(28595) About Me  (Show Source):
You can put this solution on YOUR website!
Yes because every number is in the form 7n where n is a positive integer


So take two numbers say 7n and 7m and add them to get 7n+7m=7(n+m) which is a multiple of 7, which means that this set is closed under addition.