SME
Grade 3 Math · Problem type
Find an unknown side from the area
Use this when you know the area and one side: “24 cm², 6 cm long. How wide?”
Diagram
This is an example. Type your own values to start a new problem.
Length (cm)
×
Width (cm)
=
Area (cm²)
Formulas
6 × 4 = 24
Length × width = area
Assumptions
•
The shape is a rectangle.
•
Area = length × width, so width = area ÷ length.
Step-by-step
WE KNOW
Area: 24 cm²
Length: 6 cm
FIND
width
Step 1 · Find width
6 × ? = 24
Length × width = area
Divide the area by the length.
Width = 24 ÷ 6
Think: 6 × ? = 24
Double 6: 6 + 6 = 12
Double again: 12 + 12 = 24
4 groups of 6 make 24
Width = 4 cm
Check
Put the numbers back in. Both sides should match.
6 × 4 = 24 ✓
Topic check
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Related lessons
Area and multiplication
Main lesson
Area and the distributive property
Use this to split a rectangle into two and add the areas: 6 × 8 = 6 × 5 + 6 × 3.
Area of composite figures
Use this to find the area of an L-shape made of two rectangles.
Area of a shape with a corner cut out
Use this for an L-shape: the whole rectangle take away the corner cut out.