Wednesday, 10 January 2018

RATIOS 3


The areas of two circles are in the ratio of 25:4 . Calculate the radius of the smaller circle when the radius of larger circle is 66 cm. 

solution

let R = radius of larger circle
let r = radius of smaller circle
R= 60cm, r = ? Ratio = 25:4.


For larger circle
A1 = R2 …………(i)

For smaller circle
A2 = r2 …………(ii)

A1 = R2
A2    r2

A1 = R2
A2     r2


A1 = (R/r)
A2

(A1/A2) =  (R/r)

(25/4) =  (60/r)

5 = 60                 cross multiply
2     r

(2 x 60) = (5 x r)

120 = 5r

120 = 5r
 5      5

r = 24

radius of smaller circle is 24 cm.

TRY THIS………..

NECTA 1997 QN 5(c)

The areas of two circles are in the ratio of 16:9 . Calculate the radius of the smaller circle when the radius of larger circle is 24 cm. 

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