The length and width of a rectangle are in the proportion 3:1. If the width is 3 feet, what is the length?

What will be an ideal response?

Let x = the length in feet. 3/1
Ratio of length to width is: x / 3
When length is x and width is 3 the ratio is:
Equating both ratios gives the equation:
Cross multiply to get: 3/1—x/3 x = 3 * 3
Multiply to get the length: x = 9 feet
Thus the length is 9 feet

Check: The proportion of the actual length to width is 9:3.
In fraction form this is 9/3.
This reduces to 3/1, which is the required proportion.