Monday, 22 May 2017

RATIOS 1


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 40 cm. 

solution

let R = radius of larger circle
let r = radius of smaller circle
R= 40cm, 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) =  (40/r)

5 = 40                 
2     r

(2 x 40) = (5 x r)     after cross multiply.

80 = 5r

80 = 5r
5      5

r = 16

radius of smaller circle is 16cm.

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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