[求助]问两道PREP数学题

A committee of three people is to be chosen from four married couples. What is the number of different commitees that can be chosen if two people who are married to each other cannot both serve on the commitee?

我的想法是先8人选一个C(1,8)，那这个家庭就不能再有人了，剩下6个，再C（1，6），依次类推，最后剩下4个，再C（1，4）。最后三个乘起来就是8×6×4=192.但是答案只有32，不知道正确的思路是什么？我的思路错在哪里？望大家帮我看一下，谢谢。

还有一DS题是A contractor combined X tons of gravel mixture that contained 10% gravel G, by weight,  with Y tons of gravel mixture that contained 2% of gravel G, by weight, to produce Z tons of gravel mixture that was 5% gravel G, What is the value of X?

(1) Y=10 (2) Z=16 正确答案是D，但我怎么觉得是C啊，10%X+2%Y=5%Z，应该Y和Z同时知道，才能求出X呀。盼NN解答。

我的算法供参考： 先选三个家庭 C4，3=4； 在从这三个家庭中各自出一个人，取法为2*2*2

两个步骤相乘得32

谢谢，那你觉得我的做法错在哪里呢？

哦，谢谢，我明白了。