Question:
A rope by which a cow is tethered is increased from 16 m to 23 m. How much additional ground does it have now graze?
Solution:
r1 = 16 m
r2 = 23 m
Amount of additional ground available $=$ Area of the bigger circle $-$ Area of the smaller circle
$=\pi\left(r_{1}^{2}-r_{2}^{2}\right)$
$=\pi\left(23^{2}-16^{2}\right)$
$=\pi(23+16)(23-16)$
$=858 \mathrm{~m}^{2}$
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