Question

a metal washer is shown with the following radii (plural for radius). what is the area of the metal in the washer rounded to 1 decimal place? use \\( \pi = 3.142 \\)

Explanation:

Step1: Recall the formula for the area of an annulus (washer)

The area of a washer (annulus) is given by the formula \( A=\pi(R^{2}-r^{2}) \), where \( R \) is the outer radius and \( r \) is the inner radius. Here, \( R = 20\space mm \) and \( r=10\space mm \), and \( \pi = 3.142 \).

Step2: Substitute the values into the formula

First, calculate \( R^{2}-r^{2} \):
\( R^{2}-r^{2}=20^{2}- 10^{2}=400 - 100=300 \)

Step3: Multiply by \( \pi \)

Now, multiply the result by \( \pi \):
\( A = 3.142\times300=942.6 \)

Answer:

\( 942.6\space mm^{2} \) (corresponding to the option with 942.6 m, assuming a typo and it should be \( mm^{2} \))