Is the sum of two multiples of 7 always a multiple of 7?

using simple algebra. A multiple of 7 can be written as 7a or 7b where a, b are elements of the set of real numbers so adding them you have 7a + 7b = 7(a+b) and 7(a+b) is a multiple of 7 since a+b is rea. Try putting any value for a and b and see whether it works .(It should do)