Comparing Deals using Proportion (SQA National 5 Applications of Mathematics): Revision Note
Exam code: X844 75
Comparing deals using proportion
How do I compare deals using proportion?
There are two main methods
comparing the price per item
comparing the number of units per £1
Price per item or unit
STEP 1
Find the price of 1 unit by dividing each price by the number of units in that deal50 litres for £3.20
£3.20 ÷ 50 = £0.064 per lite
30 litres for £1.95
£1.95 ÷ 30 = £0.065 per lite
STEP 2
Choose the deal which has the lowest price per unit£0.064 < £0.065
50 litres for £3.20 is the better deal
Number of units per £1
STEP 1
Find the number of units per £1 by dividing the number of units in each deal by the price of that deal50 litres for £3.20
50 ÷ £3.20 = 15.625 litres per £1
30 litres for £1.95
30 ÷ £1.95 = 15.384... litres per £1
STEP 2
Choose the deal which has the highest amount per £115.625 > 15.384...
50 litres for £3.20 is the better deal
Worked Example
3 caps for £22.50 from Baseball World
5 caps for £36 from Head Hut
At which shop are the caps better value?
You must show your working.
Answer:
Method 1
STEP 1
Find the price of 1 cap for each deal
£22.50 ÷ 3 = £7.50 for 1 cap from Baseball World
£36 ÷ 5 = £7.20 for 1 cap from Head Hut
STEP 2
Choose the deal which has the lowest price
£7.20 is cheaper than £7.50
Head Hut is better value
Method 3
STEP 1
Find the number of caps per £1
3 ÷ £22.50 = 0.133... caps per £1 from Baseball World
5 ÷ £36 = 0.138... caps per £1 from Head Hut
STEP 2
Choose the deal which has the highest number of caps per £1
0.138... is bigger than 0.133...
Head Hut is better value
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