请教prep模考软件上的一道数学题

leonan

有道prep模考软件上的数学题很纠结，请各位帮忙解释下，谢谢！
原题大概如下：
DS:  500 is a multiple of 100 that is the nearest to x, 400 is a multiple of 100 that is the nearest to y, what is the multiple of 100 that is the nearest to x+y?
1) x< 500
2) y<400
题目没有读懂，请大家指教，谢谢！

xpxmw

答案是选C 么

leonan

好象是选C，请解释下呀，谢谢！