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Cogito

Grade 3 Math · Chapter 4 · Lesson 3

Practice Worksheet

Finding a Missing Side

Working backwards from the area.

10 problems · about 12 minutes · 3.MD.C.7

NameDate

Figure — use these to answer the problems

Set one side and watch which area it gives.

Area · squares inside

24

Perimeter · walk around

20

6 × 4 = 24 · 6 + 4 + 6 + 4 = 20

Known side6
Other side4
Figure 1

Warm-Up Review

From earlier lessons. Loosen up before the new work.

3 problems

  1. From “Area by Multiplying”

    A rectangle 8 by 7. What is its area?

    Answer

  2. From “What Area Is”

    A rectangle 7 across and 3 down. What is its area?

    Answer

  3. From “Two-Step Problems With a Letter”

    8 × 5 − 14 = ?

    Answer

Warm Up

Straightforward practice. Get the method working first.

3 problems

  1. Area 42, one side 6. What is the other side?

    Answer

  2. What kind of question is finding a missing side?

    • A missing factor question.
    • An adding question.

  3. Area 24, one side 6. What is the other side?

    Answer

Build It Up

The same ideas with more to keep track of.

1 problem

  1. Area 45, one side 9. What is the other side?

    Answer

Stretch Yourself

Mixed problems. Work out what kind of question it is before you start.

3 problems

  1. Area 56, one side 7. What is the other side?

    Answer

  2. The Garden Bed

    A bed has an area of 32 square metres and is 4 metres wide. How long is it?

    Answermetres

  3. The Sticker

    A sticker has an area of 18 square cm and is 3 cm tall. How wide is it?

    Answercm