Math PicnicFree printable practice

Find a side from the area worksheets

If a rectangle covers 48 square centimeters and one side is 6, the other has to be 8 — because 6 times 8 is 48. These free printable worksheets run the area formula backward, every figure marked with A, so the move is always to divide.

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Find a side from the area
Find a side from the area worksheet — Sides to 35 cm, free printable with answer key

The answer key prints on a separate page.

What's on this sheet

The mixed missing-side sheets switch between area and perimeter, so a child has to read the figure and choose a method. This one is area throughout: the rectangle shows A and one side, and the missing side is the area divided by the side you were given. One operation, repeated, is what makes the reverse reading of the formula stick before it is mixed with anything else.

Why this sheet works

Every rectangle is built from two whole sides, so the area divides evenly and the answer is always a whole number — never 7.5. The figure carries the letter A with the number so a child reads area rather than guessing, which is also their first meeting with a formula being used in reverse.

How this one works

One question from this sheet, worked through a step at a time.

Missing side: area 195, one side 13

13 × ? =195
× is undone by ÷
195 ÷ 13 =15 cm
check: 13 × 15 =195
  1. Forwards, area is one side times the other: 13 × ? = 195. Every number you need is here, which is exactly why the usual mistake is to multiply them.
  2. But the 195 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.
  3. 195 ÷ 13 = 15 cm. Check it forwards: 13 × 15 = 195, which is what the question said.

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