PREP1　ＭＡＴＨ模拟错题６道请教！

谢谢LISY!!! 太粗心了, 少看了题目的at least. 下题仍不太懂...

119.       12086-!-item-!-187;#058&008079

A contractor combined x tons of a gravel mixture that contained 10 percent gravel G, by weight, with y tons of a mixture that contained 2 percent gravel G, by weight, to produce z tons of a mixture that was 5 percent gravel G, by weight.  What is the value of x ?　　（Ｄ）

(1) y = 10　　　　　(2) z = 16

由题干可以得出两个方程，都是含有x,y,z的，条件1知道y的值，就只剩下两个未知数，两个方程就可以解了，同理，2是，所以选D

提干得出的两个方程是这两个吗: 10%X+2%Y=5%Z 和 X+Y=Z   这两个方程??