reto wrote:

What is the sum of the odd integers from 45 to 65, inclusive?

A. 495

B. 550

C. 555

D. 600

E. 605

CONCEPT: Sum of first n positive odd Integers (all odd integers from 1 through 2n) = n^2i.e. Sum of first 33 odd Integers from 1 through 65 (inclusive) =33^2

Also, Sum of first 22 odd Integers from 1 through 43 (inclusive) =22^2

i.e. Sum of all Odd Integers from 45 through 65 (inclusive) = 33^2 - 22^2 = (33+22)(33-22) = 55*11 = 605

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