Find an Unknown Side Length of a Rectangle
Find an Unknown Side Length of a Rectangle is a Grade 3 math skill from Eureka Math applying the inverse relationship of the area formula. When the area and one side length are known, divide the area by the known side to get the unknown side: Unknown Side = Area ÷ Known Side. This rearrangement of Area = l × w uses division as the inverse of multiplication. For example, if Area = 42 sq units and one side = 7, then the other side = 42 ÷ 7 = 6. Third graders apply this to find missing dimensions in area word problems.
Key Concepts
To find an unknown side length of a rectangle when the area and one side length are known, divide the area by the known side length. This is the inverse relationship of the area formula ($Area = length \times width$).
$$Unknown\ Side\ Length = Area \div Known\ Side\ Length$$.
Common Questions
What is the formula to find an unknown side length of a rectangle?
Unknown Side Length = Area ÷ Known Side Length. This rearranges the formula Area = length × width.
If a rectangle has area 56 square units and one side of 8 units, what is the other side?
56 ÷ 8 = 7 units.
Why is dividing area by the known side equivalent to finding an unknown factor?
The area formula is multiplication: Known × Unknown = Area. To find the unknown factor, divide both sides by the known: Unknown = Area ÷ Known.
How is this skill different from Skill 44 (Finding an Unknown Side Length)?
Both use the same formula: Unknown = Area ÷ Known Side. This skill emphasizes the division formula explicitly: Unknown Side = Area ÷ Known Side.
In which textbook is Find an Unknown Side Length of a Rectangle taught?
This skill is taught in Eureka Math, Grade 3.