Question

The diameters of two circles are in the ratio 2 5

The area of the larger circle is 450 cm?
Work out the area of the smaller circle
​

Answer 1

72 cm²

Explanation:

Given the ratio of diameters = a : b , then

ratio of areas = a² : b²

Here the ratio of diameters = 2 : 5 , then

ratio of areas = 2² : 5² = 4 : 25

let x be the area of smaller circle then using proportion

`(25)/(450)` =
`(4)/(x)` ( cross- multiply )

25x = 1800 ( divide by 25 )

x = 72

That is the area of the smaller circle is 72 cm²

Answer 2

180

Explanation:

2:5

? : 450

5u-> 450

1u->90

2u-> 180