Question

A garrison of 2800 men has provision for 36 months at the rate of 396 gm per man per day. How many men should leave so that the same provisions may last for 42 months at the rate of 432gm per day?
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Answer 1

Let the number of remaining men be x
More months $\to$ less men $\to$ inverse ratio
More food per man $\to$ less men $\to$ inverse ratio

Months 42 : 36 :: 2800 : x
Food per man per day 432 : 396
$So,x=\frac{(2800\times 36\times 396)}{(42\times 432)}=2200$
Hence, the number of men to leave the garrison = 2800 – 2200 = 600.