Question:
Assuming the earth to be a sphere of radius 6370 km, how many square kilometers is the area of the land if three-fourths of the earth’s surface is covered by water?
Solution:
$3 / 4^{\text {th }}$ of earth surface is covered by water
Therefore $1 / 4^{\text {th }}$ of earth surface is covered by land
Therefore Surface area covered by land $=1 / 4 \times 4 \pi r^{2}$
$=1 / 4 \times 4 \times 22 / 7 \times(6370)^{2}$
$=127527400 \mathrm{~km}^{2}$