9 men can do a work in 12 days working 4 hours a day. In how many days can 6 men do the same work, working 8 hours a day?
18
9
10
8
Explanation:
Let d be the number of days it took to complete the work if 6 men do the same work, working 8 hours a day
If M1 men can do the work in working H1 hours per day and M2 men can do the same work in working H2 hours per day, then
M1H1=M2H2
=> $ 9 \times 12 \times 4 $ =$6 \times 8 \times d $
=>d=$\dfrac{9 \times 12 \times 4 }{48}$
=>d= 9 days
Let d be the number of days it took to complete the work if 6 men do the same work, working 8 hours a day
If M1 men can do the work in working H1 hours per day and M2 men can do the same work in working H2 hours per day, then
M1H1=M2H2
=> $ 9 \times 12 \times 4 $ =$6 \times 8 \times d $
=>d=$\dfrac{9 \times 12 \times 4 }{48}$
=>d= 9 days