How to see it
Three steps. One: add the parts to find the total. Two: divide the amount by the total parts to find one part. Three: multiply for each person. A bar model keeps it clear.
A worked example
3 plus 5 is 8 parts. £120 divided by 8 is £15 a part. Three parts: £45. Five parts: £75. Check: 45 plus 75 is 120.
The common mistake: dividing by each number separately
The trap is doing 120 divided by 3 and 120 divided by 5, which gives 40 and 24. Those do not add up to 120. The amount is shared out of 8 parts, not 3 and 5 on their own.
Try one
Share 72 sweets in the ratio 4 to 5. How many does the bigger share get?
- A40
- B32
- C36
- D45
Show the answerHide the answer
Right: A, 40
Nine parts, 8 each. Five lots of 8.