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1. Four gardeners with four grass mowers mow 400 sq. m of ground in 4 hours. How long would it take for eight gardeners with eight grass mowers to mow 800 sq. m of ground ?

A. 4 hours

B. 6 hours

C. 8 hours

D. 12 hours

Solution:

Since each gardener would work with one grass mower,
So, we shall consider 1 gardener and 1 grass mower as one unit.
Let the required time be x hours
More gardeners and grass mowers, Less time (Indirect proportion)
More area, More time (Direct proportion)

\begin{matrix} Gardeners &  grass mowers 8 : 4 \\ Area 400 : 800 \end{matrix}} :: 4 : x

\begin{aligned} ∴ 8 \times 400 \times x = 4 \times 800 \times 4 \\ \Leftrightarrow x = \frac{(4 \times 800 \times 4)}{(8 \times 400)} \\ \Leftrightarrow x = 4 \end{aligned}

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