The ratio of the radii of two wheel is 2:5. What is the ratio of their circumferences ?

Given: The ratio of the radii of two-wheel is 2:5

To do: Find the ratio of their circumference.

Solution:

Let the two radii be $r_1,r_2$

$r_1 : r_2 = 2 : 5$

Circumference of circle  =  2πr

The ratio of their circumferences  =   $2πr_1 : 2πr_2$

= $2π (2) : 2π (5)$             [ Substitute the ratios of radii in formula]

=   2  :  5                              [2π and 2π gets cancelled, since they are same]

So, the ratio of their circumferences  =  2: 5

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