Carcass wrote:
The sum of the first 50 positive even integers is 2550. What is the sum of even integers from 102 to 200 inclusive?
A. 5,100
B. 7,550
C. 10,100
D. 15,500
E. 20,100
The sum of the first 50 positive even integers is 2550. In other words,
2 + 4 + 6 + 8 + ...+ 98 + 100 = 2550We want the sum:
102 + 104 + 106 + . . . 198 + 200IMPORTANT: Notice that each term in this sum is 100 GREATER than each term in the
first sum.
In other words,
102 + 104 + 106 + . . . 198 + 200 is the SAME AS...
(
100 + 2) + (
100 + 4) + (
100 + 6) + ... + (
100 + 98) + (
100 + 100)
We can rearrange these terms to get: (
100 +
100 + ... +
100 +
100) + (
2 + 4 + 6 + 8 + ...+ 98 + 100)
IMPORTANT: There are 50
100's in the
red sum, and we're told that the
blue sum =
2550So, our sum = 50(
100) +
2550 = 5000 + 2550
= 7550
Answer: B