Tom is 7n years old now. His mother is 3 times as old as Tom. His father is 5 years older than his mother. Give your answers in terms of n.
- How old is his father now?
- What was the total age of the three family members 4 years ago?
Need a hint?
Find the mother's age first, then the father's. For part (b), remember all three people were 4 years younger.
Worked answer
- (a) Tom = 7n, so mother = 3 × 7n = 21n.
- (a) Father = 21n + 5 (5 more than the mother).
- (b) Total now = 7n + 21n + (21n + 5) = 49n + 5.
- (b) Each person was 4 years younger, so take off 4 × 3 = 12.
- (b) Total 4 years ago = 49n + 5 - 12 = 49n - 7.
Answer: 49n - 7 years
The mistake this question tests
Habit
Calculation slip
Pupils subtract 4 only once, from the total, giving 49n + 1, or they forget that the father is 5 more than the mother and write 21n instead of 21n + 5.
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