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1. Working 8 hours a day, 12 men can do a work in 30 days. Working 4 hours a day, 18 men can do work in ?

A. 30 days

B. 40 days

C. 45 days

D. 50 days

Solution:

Let the required number of days be x
Less working hours, More days (Indirect Proportion)
More men, Less days (Indirect Proportion)

\begin{matrix} Working hours 4 : 8 \\ Men 18 : 12 \end{matrix}} :: 30 : x

\begin{aligned} ∴ 4 \times 18 \times x = 8 \times 12 \times 30 \\ \Leftrightarrow x = \frac{(8 \times 12 \times 30)}{(4 \times 18)} \\ \Leftrightarrow x = 40 \end{aligned}

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