Uvero — STEM Learning

Finding Missing Sides from Perimeter

Perimeter is the total distance around a shape; a missing side is found by subtracting known sides from the total. Include every boundary segment exactly once. A careful solution names the quantities, keeps place value or units visible, and explains why each operation fits.

Worked reasoning

$2l+2w=30$ , so $18+2w=30$ .
$2w=12$ , hence $w=6$ cm.

A rectangle has perimeter 30 cm and length 9 cm. Find its width.

Which statement best captures the central mathematical idea in Finding Missing Sides from Perimeter?

Include every boundary segment exactly once.

A familiar-looking calculation may be used without checking place value, units, conditions or what the answer represents.

A memorised formula is valid even when its conditions are not met.

The diagram or notation replaces the need to justify each mathematical step.

When starting a problem about Finding Missing Sides from Perimeter, which move is most reliable?

Represent the given information clearly and identify the operation or relationship required for finding missing sides from perimeter.

Round every value before identifying the mathematical structure.

Choose the longest available formula and substitute immediately.

Assume the desired conclusion and work backwards without checking equivalence.

Which statement is a misconception that must be rejected when working with Finding Missing Sides from Perimeter?

A familiar-looking calculation may be used without checking place value, units, conditions or what the answer represents.

Include every boundary segment exactly once.

Represent the given information clearly and identify the operation or relationship required for finding missing sides from perimeter.

Estimate first, then reverse the operation or use a second representation to check that the answer is reasonable.