Algebra 2 - Arithmetic

Question

2+4+10+___+142.

It's arithmetic and I need to show work. I don't understand how to do it.

Answer 1

this is obviously 2(1+2+3+...+71).

you should know the formula for sum of first n positive integers = n(n+1)/2

so the quantity inside the parentheses equals 71(72)/2 and this should be enough to help you obtain

the answer; your series sum is 71(72) -- right?