8 : 125
2 : 5
8 : 25
4 : 25
4 : 10
Correct answer is D
surface area of formula = πr2
If the radius is reduced then let its radius be x.
Its area is πx2 .
x : r = 2 : 5,
so xr = 25
→ 5x = 2r
Hence, x = 0.4r.
Hence the area of the new circle is π (0.4r)2 = 0.16π r2 .
The ratio of the two areas is
0.16πr2 : πr2
= 0.16 : 1 = 16 : 100
= 4 : 25.
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