Method · Volume working backwards

  1. 1.Write the formula: V = length × width × height
  2. 2.Plug in what you know
  3. 3.Rearrange to find the missing side

Example · Different numbers

Pretend a different cuboid has volume 120 cm³, length 4 cm, width 3 cm. Find the height.

4 cm3 cmh = ?V = 120 cm³
Step 1 — formula:
V = l × w × h
Step 2 — plug in:
120 = 4 × 3 × h
Step 3 — simplify and rearrange:
120 = 12 × h
h = 120 ÷ 12
h = 10 cm

Notice: I divided the volume by the two known sides multiplied together. That’s the “working backwards” bit.

Now your turn.Same method, your numbers (V = 400, sides 8 and 10). What’s your step 1?

OK, my turn