Missing sideArea or perimeter
Name: Date:
Find the missing side. All lengths are in centimeters.
1 cm
2 cm
3 cm
4 cm
5 cm
6 cm
7 cm
8 cm
Missing side length worksheets
Knowing that area is length times width is one thing. Using it backwards is another. These free printable worksheets print the area or the perimeter inside the rectangle and leave one side as a question mark.
If they get stuck
Missing side length
The answer key prints on a separate page.
What's on this sheet
The figure says which measurement it is giving you. A rectangle marked A = 48 and a rectangle marked P = 48 are different questions with different answers, so the letter is printed with the number rather than left to be guessed. That small piece of notation is also a child's first meeting with a formula being read in reverse.
Why this sheet works
Working backwards from the area means dividing; working backwards from the perimeter means halving and then subtracting. Mixing the two on one sheet is the hardest and most useful setting, because the child has to read the figure before choosing a method rather than applying the same move eight times.
How this one works
Missing side: area 342, one side 19
19 × ? =342
× is undone by ÷
342 ÷ 19 =18 cm
check: 19 × 18 =342
- Forwards, area is one side times the other: 19 × ? = 342. Every number you need is here, which is exactly why the usual mistake is to multiply them.
- But the 342 is the ANSWER to that multiplication, not another side. To get back to the missing one, undo the multiply — and the undo of multiplying is dividing.
- 342 ÷ 19 = 18 cm. Check it forwards: 19 × 18 = 342, which is what the question said.