L2 · Finding a missing base or height

Learning goal

“I can find a missing base or height of a parallelogram when I know its area and the other dimension - by dividing, and by checking my answer with multiplication.”

Inverse operation — an operation that undoes another: division undoes multiplication.

Missing dimension — the base or height you are solving for when the area is known.

Check by multiplying — after dividing, multiply your answer by the known dimension; you must land back on the area.

Worked example

A parallelogram has area 48 cm2 and height 6 cm. Find the base. Step 1: The formula says area = base x height, so 48 = base x 6. Step 2: Division is the inverse of multiplication. Base = 48 / 6 = 8 cm. Step 3 - Check by multiplying: 8 x 6 = 48. On the grid, the rearranged rectangle is 8 cm long and 6 cm wide, and it really does hold 48 squares. Say it plainly: finding a missing dimension always means dividing the area by the known dimension - never multiplying.

Check yourself — explain it

Why do we divide to find the missing base?

Paired problem — example still visible

Area 35 cm2, base 7 cm. Find the height. -> Height = 35 / 7 = 5 cm (check: 7 x 5 = 35)

Faded completion — last step is yours

"Area 54 cm2, height 9 cm: base = 54 / ___ = ___ cm" -> 9; 6 cm

Ready to practise?

10 scored questions with a 3-rung hint ladder. Mastery needs 8/10 plus both gate questions.

Start practice →Take the unit quiz