PREP上的一道数学题，百思不得其解

Iris780

If x is equal to the sum of the even integers from 40 to 60, inclusive, and y is the number of even integer from 40 to 60, inclusive, what is the value of x+y?
a.550
b.551
c.560
d.561
e.572
最好有具体过程，感激不尽~~

135759

y=(60-40)/2+1=11
x=(40+60)*11/2=550
x+y=561

Iris780

y=(60-40)/2+1=11
x=(40+60)*11/2=550
x+y=561

-- by 会员 135759 (2012/3/8 11:00:16)

谢啦