Question

Mario computes the circumference of his 15” wide bicycle tire as 23.55 inches. What was his error?

He multiplied by the diameter instead of the radius.

He squared the radius instead of doubling it.

He used the radius instead the diameter.

He multiplied the diameter and radius in the formula.

Answer 1

He used the radius instead the diameter.

Explanation:

Mario computes the circumference of his 15” wide bicycle tire as 23.55 inches.

15 inches wide means the diameter is 15 inches. The radius is
`15/2=7.5` inches

And the circumference is found as =
`2\pi r`

Where r is 7.5

The circumference is =
`2*3.14*7.5=47.1`inches

But Mario computed is as 23.55, this is half of 47.1

This means he just multiplied pi and 7.5, rather than
`2\pi r`.

So, the correct option is : He used the radius instead the diameter.

Answer 2

we know that

[the length of a circumference]=2*pi*r-------> pi*D
i Diameter D=15 in
[the length of a circumference]=pi*15------> 47.1 in

therefore

the answer is
He used the radius instead the diameter.