If integer k is equal to the sum of all even multiples of 15 between 390 and 615, what is the greatest prime factor of k?  Answers:	A) 5	B) 7	C) 8	D) 13	E) 17
if we break down what the stem is asking what is the sum of all mult of 30 between 390 and 600.   using arithmetic progression to find n : 600 = 390 + (n - 1) 30   210+ 30 = 30n   240 = 3n =&gt; n = 8   the sum would be: 8* mean   mean = [600 + 390] / 2 = 495   8*495   8
<result>C</result>
If integer k is equal to the sum of all even multiples of 15 between 390 and 615, what is the greatest prime factor of k?