If X is the sum of first 30 positive even integers and Y is the sum of first 30 positive odd integers, what is the value of x-y?
Please try to explain your answers
Options:
(A) 10
(B) 25
(C) 30
(D) 75
(E) 100 Stream of consciousness:
user
First even minus first odd = 2-1 = 1;
The sum of first 2 even integers minus the sum of first 2 odd integers = (2+4)-(1+3) = 2;
The sum of first 3 even integers minus the sum of first 3 odd integers = (2+4+6)-(1+3+5) = 3;
We can see the patterns here, so the sum of first 30 positive even integers minus the sum of first 30 positive odd integers will be 30.
Thus, the answer is (C).
assistant