Q. 65.0( 3 Votes )
On decreasing the radius of a circle by 30%, its area is decreased by
A. 30%
B. 60%
C. 45%
D. none of these
Answer :
Let the radius if circle be r
Area of circle = A = πr2
Radius decreases by 30%
So, New Radius r’ = r - 30/100 × r = 0.7r
New Area of circle = A’ = πr’2 = π × (0.7r)2
= .49πr2
Percentage decrease in area = 
= 
= .51 × 100 = 51
∴ Decrease in area = 51%
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