Set M consists of the consecutive integers from -15 to y, inclusive. If the sum of all the integers in set M is 70, How many numbers are in the set?

Question

SAT prep help - Anonymous, Saturday, September 28, 2013 at 3:16pm
a. 33
b. 34
c. 35
d. 36
e. 37

Answer 1

There are y+16 integers. We just want to sum an arithmetic sequence where
a = -15
d = 1 and find how many terms there are:

(y+16)/2 (-30+(y+15)*1) = 70
y = 19

So there are 19+16=35 terms