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1. 5 persons can prepare an admission list in 8 days working 7 hours a day. If 2 persons join them so as to complete the work in 4 days, they need to work per day for ?

A. 8 hours

B. 9 hours

C. 10 hours

D. 12 hours

Solution:

Let the number of working hours per day be x
More persons, Less working hours ( Indirect proportion)
Less days, More working hours (Indirect proportion)

\begin{matrix} Persons   7 : 5 \\ Quantity  4 : 8 \end{matrix}} :: 7 : x

\begin{aligned} ∴ 7 \times 4 \times x = 5 \times 8 \times 7 \\ \Leftrightarrow x = \frac{(5 \times 8 \times 7)}{(7 \times 4)} \\ \Leftrightarrow x = 10 \end{aligned}

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