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1. 15 men take 21 days of 8 hours each to do a piece of work. How many days of 6 hours each would 21 women take, 3 women do as much work as 2 men ?

A. 18

B. 20

C. 25

D. 30

Solution:

3 women ≡ 2 men
So, 21 women ≡ 14 men
Less men, More days (Indirect proportion)
Less hours per day, More days (Indirect proportion)

\begin{matrix} Men 14 : 15 \\ Hours per day 6 : 8 \end{matrix}} :: 21 : x

\begin{aligned} ∴ (14 \times 6 \times x) = (15 \times 8 \times 21) \\ \Leftrightarrow x = \frac{(15 \times 8 \times 21)}{(14 \times 6)} \\ \Leftrightarrow x = 30 \end{aligned}

∴ Required number of days = 30

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