Finding a percentage of a quantity is in the Primary 5 Percentage chapter. The lesson film below teaches it with its own questions, and the practice set is written for Primary 5.
Lesson video, with the working
Finding a percentage of a quantity
3 min 01 s
The film teaches 2 questions in turn. Each question shows first; its working is written as the film explains it.
A stall sold 400 chicken rice sets in one month. 40% of them were takeaway orders. How many of the sets were takeaway orders?
40% of 400 sets is 160 sets.
Ans: 160
Example 1
Out of the same 400 sets, 100 were sold on a Sunday. What percentage of the sets is that?
That is 25% of the sets.
Ans: 25%
How to solve it
Draw one bar for the whole, 400 sets. The whole is always 100 percent.
To find a percentage of the whole, write the percentage over 100, then times the whole: 40 over 100, times 400.
Cancel: 100 goes into 400 four times, so it becomes 40 times 4, which is 160 sets.
To turn a part into a percentage, write the part over the whole: 100 Sunday sets over 400 sets.
Times it by 100 percent: 100 over 400, times 100 percent, is 25 percent.
To find a percentage of a whole, write the percentage over one hundred and times the whole. And to turn a part into a percentage, write the part over the whole and times one hundred percent.
Practice questions with worked solutions
Question 1 is free to try. The other 10 open in the free trial, each with its full working.
How do you solve P5 percentage of an amount questions?
Finding a percentage of an amount turns a percentage into an actual number of things, dollars or grams.
What your child learns here
Finding a percentage of an amount turns a percentage into an actual number of things, dollars or grams. This page teaches the Primary 5 method, the percentage over 100 times the whole, and sets it beside its opposite, a part written as a percentage of the whole.
Write the percentage as a fraction over 100: 40% = 40/100.
Multiply by the whole, cancelling first: 40/100 × 400 = 40 × 4 = 160.
Keep 'a percentage of' apart from 'what percentage': 40% of 400 sets is 160 sets, while 100 sets out of 400 is 25%.
For the part not taken, subtract from the whole, or use the percentage left: when 60% of the badges are sold, 40% are not.
When the whole and the answer use different units, convert first: 20% of 1.5 litres is 300 ml.
Does the answer make sense?
Use 1% as a stepping stone: 1% of 400 is 4, so 8% is 8 × 4 = 32 shuttlecocks. The size fits too, because 10% of 400 is 40, and 8% is a little less than 10%, so the answer must sit a little under 40.
How to practise these questions
Free Question 1 asks how many of a shop's 400 badminton shuttlecocks were damaged when 8% of them were. Basic questions train finding a percentage of a number of shuttlecocks, badges or chicken rice sets, including the badges that were not sold. Intermediate questions add a change from litres to millilitres, two shares of a monthly income with the savings left over, and a bag of rice where the part used is written as a percentage. Challenge questions compare percentages of two different wholes, find the gap between two colours of beads in one box, pour kilograms and grams of flour into one tub, take a percentage of what remains, or count the children who chose both of two activities. If the working goes astray, open its worked solution and try the question again later from Revision.
Questions parents ask
How do you find a percentage of a number? Write the percentage over 100 and multiply by the number. 15% of 600 is 15/100 × 600 = 90.
Is there a quicker way for easy percentages? Yes. Find 10% by dividing by 10, or 1% by dividing by 100, then scale up. 25% is also one quarter, and 50% is one half.
Which part of the syllabus is this? Finding a percentage part of a whole, a Primary 5 Percentage outcome. The lesson on this page also revises expressing a part as a percentage, so your child can tell the two questions apart.
