The radius of a circle is 90 cm. If the radius of this circle is increased to 99 cm, then what will be the percentage increase in the area of this circle?
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e. 21%.
Let the radius of the circle be 10x units.
Then area of circle = π × r2 = π × 100x2 units
Now as the radius is increased from 90cm to 99cm i.e. 1/10th part
Hence new assumed radius = 10x + 1x = 11x
New assumed area = π × r2 = π × 121x2 units
Percentage increase in area = π × (121x2 - 100x2)/ π × 100x2 × 100 = 21/100 × 100 = 21%