Question

# On decreasing the radius of a circle by 30 %, its area is decreased by (a) 30 %                  (b) 60 %               (c) 45%                  (d) none of these

Solution

## Let the radius of the circle be r cm So, area of the circle = πr2 Now, radius decrease by 30% So, the new radius = 0.7r  Area of the circle with new radius = π(0.7r)2 = 0.49r2π Change in the area =  πr2 - 0.49r2×π  = 0.51r2 ×π % change in area = 0.51×r2×πr2×π × 100%  = 51% Hence, the correct option is (d). MathematicsSecondary School Mathematics XStandard X

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