have trouble in doing sth 和 be used as 和 the number of 和 a n

I have trouble in doing my homework.
我做作业有困难.
He has trouble in communicating with his parents.
他跟他父母沟通很困难.
Some of the crops can be used as animal feed.
一些庄稼又可以用做动物饲料.
Anything you say may be used as evidence against you.
你说的任何话都可以被用来当作对你不利的证据.
The number of people in the world inched up.
世界人口增长了.
The number of hours everyone works should be reduced.
每个人工作的时间必须减少.
A number of students like computer games.
很多学生喜欢玩电脑游戏.
A number of people would rather stay home during the Spring Festival.
春节很多人宁可呆在家里.