Question

1. 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 multiplied the diameter and radius in the formula.
he used the radius instead the diameter.
he squared the radius instead of doubling it.

Explanation:

The formula for the circumference of a circle is \( C = \pi d \) (where \( d \) is the diameter) or \( C = 2\pi r \) (where \( r \) is the radius, and \( d = 2r \)). The tire's width is the diameter (\( d = 15 \) inches). Using the correct formula \( C=\pi d \), we get \( C = 3.14\times15=47.1 \) inches. Mario got 23.55 inches, which is \( \pi r \) (since \( 3.14\times7.5 = 23.55 \), and \( 7.5 \) is the radius). So he used the radius instead of the diameter in the formula \( C=\pi d \) (he used \( C=\pi r \) by mistake).

Answer:

C. He used the radius instead the diameter.