Arectangle with a perimeter of 40 inches has a width that is 3 times the length. what is the length?

Divide by 4, the width is 10 inches, times by 3, the length is 30 inches

To find the perimeter of a rectangle, the formula is 2*length+2*width=perimeter.
So, say that the variable x is the length. Because the width is 3 times the length x, the width is equal to 3x.
I can plug what we know into the formula.
(2*x) + (2*3x) = 40
2x + 6x = 40
8x = 40
Divide both sides by 8 to get x = 5.
So, your length is 5 inches!

(To double check, you can just plug it into the problem. (2*5) + (2*15) = 10 + 30 = 40.)