[問題]PP的問題

[angelat]

If 500 is the multiple of 100 that is closest to X and 400 is the multiple of 100 that is closest to Y, which multiple of 100 is closest to X+Y?

(1) X<500
(2) Y<400

A: E

這一題題目完全不瞭解，可以幫忙解釋嗎？謝謝