Question

A bicycle tire has a radius of 15 inches. What is the circumference of the tire? Round to the nearest tenth

Answer 1

$C = 2\pi\ r$ where C = circumfrence, r = radius, and $\pi\approx\ 3.14$.

Plug in 15 for r (our radius).
$C = 2\pi\times15$

2 × 15 = 30
$C = 30\pi$

Use 3.14 for $\pi$.
$C \approx 30\times3.14$
$C \approx 94.2$

Answer 2

To find the circumference of a circle, we use the formula
C = πd
The diameter is always double the radius
15 x 2 = 30 inches
C = 30 x π
30π = 94.277796...

To round to the nearest 10th, we look at the number after the tenth decimal place
94.2477796
If it is 5 or above, we round up
If it is 4 or less, we round down
4 < 5 therefore we round down

94.2 inches