应用题,英语!

题目

应用题,英语!
A contractor agreed to finish a project in 50days.He employed 120men who worked 9hours in a day.After 20 days,he found that only 1/3of the project was completed.How many more men should he employ to finish the work on time if each man now worked 10 hours a day?

答案

目前已经完成120*9*20=21600个人工时,相当于1/3的项目进度
因此余下的2/3项目相当于21600*2＝43200个人工时
现在起每人每天做10小时,要在30天内完成,需要43200/30/10=144人
因此,需要增加的工人人数为144-120＝24人