Question : A man and a woman can finish a work together in half the time taken by a woman and a boy together. A boy can finish the work alone in 20 days and 2 women together can finish it in 30 days. In how many days will the work be finished by 4 men?
Option 1: 2
Option 2: 2.14
Option 3: 2.5
Option 4: 3
Correct Answer: 2.14
Solution :
Given: Time taken by a man and a woman = $\frac{1}{2}$ (Time taken by a woman and a boy)
Time taken by a boy to complete the work = 20 days
Time taken by 2 women to complete the work = 30 days
Time taken by a woman to complete the work = 60 days
Let a man finish the work in $m$ days
The time taken by a woman and a boy to complete the work is $x$ days. Then, $\frac{1}x = \frac{1}{60}+\frac{1}{20}$
⇒ $x$ = 15 days
Now, time taken by a man and a woman =$\frac{15}{2}$ days
So, ${\frac{1}m+\frac{1}{60}}=\frac{2}{15}$
⇒ $m=\frac{60}7$
Time taken by 4 men to do the work $=\frac{m}4=\frac{15}{7}=2.14$ days
Hence, the correct answer is 2.14.
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