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प्रश्न
On decreasing the radius of a circle by 30%, its area is decreased by
विकल्प
30%
60%
45%
none of these
उत्तर
None of these
Let r be the original radius.
Thus, we have:
Original area = πr2
Also,
New radius = 70% of r
`=(70/100xx""r")`
`= (7"r")/10`
New area `= pixx((7"r")/10)^2`
`= (49pi"r"^2)/100`
Decrease oin the area`=(pi"r"^2 = (49pi"r"^2)/100)`
`=(59pi"r"^2)/100`
Thus, we have;
Decrease in the area`=((59pi"r"^2)/100xx1/pi"r"^2xx100)%`
= 51%
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