All 6 problems from "Percentages" with complete step-by-step worked solutions: recognising the type, the idea, the working steps and the conclusion. Use this page to review with your child after the animated lesson, or let them check their own working against it.
A library has 300 books. 10% of them are comic books. How many comic books are there?
Key idea: Find 1% first (divide by 100), then scale up.
10% of 300 books — a percent-of-a-quantity problem.
Go through 1%: 1% of 300 is 3 books.
1% of 300 = 300 ÷ 100 = 3.
10% = 3 × 10 = 30.
So: So there are 30 comic books.
What is 50% of 240 metres?
Key idea: Find 1% first (divide by 100), then scale up.
50% of 240 metres.
1% first, then multiply by 50.
1% = 240 ÷ 100 = 2.4 m.
50% = 2.4 × 50 = 120 m.
So: So 50% of 240 metres is 120.
What is 25% of 200 kg?
Key idea: Find 1% first (divide by 100), then scale up.
25% of 200 kg.
1% of 200 kg is 2 kg; scale up to 25%.
1% = 200 ÷ 100 = 2 kg.
25% = 2 × 25 = 50 kg.
So: So 25% of 200 kg is 50 kg.
A depot stores 500 kg of cement. 60% of it has been used. The amount used is ___ kg.
Key idea: Find 1% first (divide by 100), then scale up.
60% of 500 kg of cement has been used.
1% of 500 is 5 kg; scale up to 60%.
1% = 500 ÷ 100 = 5 kg.
60% = 5 × 60 = 300 kg.
So: So the amount used is 300 kg.
30% of a number is 90. What is the number?
Key idea: Work backwards: from a percent, find 1%, then the whole 100%.
30% of an unknown number is 90 — the whole number is asked for.
If 30% is worth 90, then 1% is 90 ÷ 30.
1% = 90 ÷ 30 = 3.
The whole (100%) = 3 × 100 = 300.
So: So the number is 300.
A shop has 400 metres of fabric. It sells 35% in the morning and 25% in the afternoon. How many metres are left?
Key idea: For “how much is left”, combine the used percents first, then take the rest of 100%.
35% of 400 m sold in the morning and 25% in the afternoon — how much is left?
Sold: 35% + 25% = 60%, so 40% remains; find it via 1%.
Left = 100% − 60% = 40%.
1% of 400 m = 4 m.
40% = 4 × 40 = 160 m.
So: So 160 metres are left.
A shop has 200 kg of rice. In the morning it sells 25% of the rice. How many kilograms of rice does it sell in the morning?
Shortcuts: Space (play), Arrow keys (step), R (reset), F (fullscreen)
A shop has 200 kg of rice. In the morning it sells 25% of the rice. How many kilograms is that? Quick guess: is it exactly 25 kg? The grid has exactly 100 cells — one for each percent of the rice.
Percent problems become easy when the whole is drawn as 100 equal cells.
Change the numbers and watch the diagram redraw itself:
