PQRS is a rectangle. The ratio of the sides PQ and QR is 3 :1. If the length of the diagonal PR is 10 cm, then what is the area (in cm$$^2$$) of the rectangle?
Let say, PQ=3k and QR=k .
So, $$\left(3k\right)^2+k^2\ =10^2\ .$$
or, $$k^2\ =5^2\ .$$
or, $$k\ =5\ .$$
So, PQ=15 cm  and QR=5 cm.
So, Area=Â $$PQ\times QR=15\times5=75\ cm^2\ .$$
C is correct choice.
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