math
posted by M .
The 20 leaves of a 40page book are numbered 1 through 40. The first and last leaves are ripped out. What is the sum of the remaining page numbers?

So what is the sum of 3+4+5+...37+38 ?
It is an arithemetic sum, first term 3, d=1
http://en.wikipedia.org/wiki/Arithmetic_progression
n= 36 terms
Sum= n/2 (2a+(n1)d) 
I got 738