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1. 39 persons can repair a road in 12 days, working 5 hours a day. In how many days will 30 persons, working 6 hours a day, complete the work?

A. 10

B. 13

C. 14

D. 15

Solution:

Let the required number of days bex.
Less persons, More days (Indirect Proportion)
More working hours per day, Less days (Indirect Proportion)

\begin{matrix} Persons 30 : 39 \\ Working hour/day 6 : 5 \end{matrix}} :: 12 : x

\begin{aligned} ∴ 30 \times 6 \times x = 39 \times 5 \times 12 \\ \Rightarrow x = \frac{39 \times 5 \times 12}{30 \times 6} \\ \Rightarrow x = 13 \end{aligned}

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