Answers

2016-07-25T20:24:34+08:00
I kinda interpret it this way
10.5 hours ...
3 men take 5 hrs to make 2 identical trenches.
3 men x 2 identical trenches = 5 hours
3 men x 1 trench = 2.5 hours
1 man x 1 trench = 7.5 hours
7.5 hours = work rate of one man
7.5 hours ÷ 5 = work rate of 5 men
work rate of 5 men = 1.5 hours
1.5 hours x 7 identical trenches = 10.5 hours
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