CoreIn almost every paper that tests this subjectAbout 60 seconds a question in the test
The big idea
A ratio compares quantities. In the ratio 2 : 3 there are 5 parts in total.
To share an amount in a ratio: add the parts, find one part, then multiply. For recipes, work out the amount for one person first (the unitary method).
Tips that save marks
Write the total number of parts before you start.
Check your shares add up to the original total.
Ratios can be simplified like fractions: 6 : 9 = 2 : 3.
A worked example
Share £40 in the ratio 3 : 5.
3 + 5 = 8 parts.
£40 ÷ 8 = £5 per part.
Shares: £15 and £25.
Now try five
Try each one before you look at the answer: answering from memory is what makes it stick. Tap an option to check it. Most children get three or four right at first; five out of five means move on to the next topic.
Question 1Aim for about 60 seconds
1 kg is about 2.2 lbs. About how many kilograms are there in 15.4 lbs?
Show the worked answer
Answer: A, 7 kg
How to work it out
Each kilogram is 2.2 lbs, so divide: 15.4 ÷ 2.2 = 7.
Check: 7 × 2.2 = 15.4.
Why the other options are wrong
B (13 kg): This takes away 2.2 instead of dividing by it.
C (6 kg): Check by multiplying your answer by 2.2.
D (34 kg): This multiplies by 2.2 again. Changing pounds to kilograms makes the number smaller.
E (8 kg): Check by multiplying your answer by 2.2.
Question 2Aim for about 60 seconds
A recipe for 6 people uses 450 g of flour. How much flour is needed for 9 people?
Show the worked answer
Answer: A, 675 g
How to work it out
Flour for one person: 450 ÷ 6 = 75 g.
For 9 people: 75 × 9 = 675 g.
Question 3Aim for about 60 seconds
A recipe for 8 people uses 200 g of flour. How much flour is needed for 24 people?
Show the worked answer
Answer: D, 600 g
How to work it out
Flour for one person: 200 ÷ 8 = 25 g.
For 24 people: 25 × 24 = 600 g.
Question 4Aim for about 60 seconds
On a map, 1 cm stands for 3 km. Two villages are 6 cm apart on the map. How far apart are they in real life?
Show the worked answer
Answer: C, 18 km
How to work it out
Each centimetre is 3 km, so 6 cm is 6 × 3 = 18 km.
Why the other options are wrong
A (9 km): This adds the numbers; each centimetre is worth the scale.
B (2 km): This divides by the scale; it should multiply.
D (19 km): A near miss: check the working again.
E (180 km): One zero too many.
Question 5Aim for about 60 seconds
A recipe for 4 people uses 150 g of flour. How much flour is needed for 8 people?
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