Question

The ratio of the radii of two wheels is 4 : 5. What is the ratio of their circumference?

• A. 4 : 5
• B. 5 : 4
• C. 2 : 5
• D. 5 : 2

Answer 1

The correct option is B 5 : 4

Let the radii of the two cicles be 5$x$ and 4$x$ respectively.
So the circumference of first circle = 2 $\pi$ r = 2 $\pi$ x 5$x$ = 10 $\pi$ $x$
The circumference of the second circle = 2 $\pi$ r = 2 $\pi$ x 4$x$ = 8 $\pi$ $x$
The ratio of the circumferences of the two circles
= 10 $\pi$ $x$ : 8 $\pi$ $x$
= 10 : 8
= 5 : 4