Rectangle Perimeter 1

Task

To compute the perimeter of a rectangle you add the length, $l$ and width, $w$ and double this sum.

1. Write an expression for the perimeter of a rectangle.
2. Use the expression to find the perimeter of a rectangle with length 30 and width 75.

IM Commentary

This tasks gives a verbal description for computing the perimeter of a rectangle and asks the students to find an expression for this perimeter. They then have to use the expression to evaluate the perimeter for specific values of the two variables. In this problem, the variable names $l$ and $w$ convey the meaning of length and width of a rectangle. A follow up to this task is Rectangle Perimeter 2, where students are asked to determine if expressions for the perimeter of a rectangle are correct and equivalent.

Attached Resources

Solution

1. The description for computing the perimeter of a rectangle first adds the length $l$ and the width $w$ of the rectangle $$l+w$$ Then it asks us to double this sum, that means we are taking the sum and multiplying it by $2$: $$\mbox{perimeter of a rectangle} = 2(l+w)$$
2. Letting $l=30$ and $w=75$ we have $$\mbox{perimeter of this rectangle} = 2(30+75)=2(105) = 210.$$