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Question : 12 men can do work in 8 days while 4 boys can do it in 40 days. In how many days 9 boys and 3 men together will complete the same work?

Option 1: 10 days

Option 2: $\frac{280}{13}$ days

Option 3: $\frac{80}{7}$ days

Option 4: $\frac{260}{17}$ days


Team Careers360 2nd Jan, 2024
Answer (1)
Team Careers360 24th Jan, 2024

Correct Answer: $\frac{80}{7}$ days


Solution : 12 men can do work in 8 days while 4 boys can do it in 40 days.
$M_{1}D_{1} = M_{2}D_{2}$
$⇒ 12 \text{ men} \times 8 = 4 \text{ boys} \times 40$
$⇒ 12 \text{ men} = 4 \text{ boys} \times\frac{40}{8}$
$⇒ 3 \text{ men} = 5 \text{ boys}$
$⇒ 1 \text{ man} = \frac{5}{3} \text{ boys}$
Now in the second case, 4 boys can do work in 40 days.
1 boy can do the work in 40 × 4 days = 160 days
9 boys and 3 men = $9 + \frac{5}{3} \times 3$ boys
9 boys and 3 men = 14 boys
14 boys can do in = $\frac{160}{14} = \frac{80}{7}$ days.
Hence, the correct answer is $\frac{80}{7}$ days.

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