Carcass wrote:
What is the sum of odd integers from 35 to 85, inclusive?
A) 1,560
B) 1,500
C) 1,240
D) 1,120
E) 1,100
One approach
We want: 35 + 37 + 39 + 41 + . . . . 79 + 81 + 83 + 85
Add the numbers
in pairs, starting from the outside and working towards the middle, we get:
35 + 37 + 39 + 41 + . . . . 79 + 81 + 83 + 85 = (35 + 85) + (37 + 83) + (39 + 81) + . . .
= (120) + (120) + (120) + (120) + .....
= 120
times some integer
So, the desired sum
must be DIVISIBLE by 120Only one answer choice is divisible by 120
Answer: A