A bag of marbles was shared among three children. Hui Min received 9n marbles. Carlos received 3 fewer marbles than Hui Min. Dev received twice as many marbles as Carlos.
- How many marbles did Dev receive? Give your answer in terms of n.
- How many marbles did the three children receive altogether when n = 5?
Need a hint?
For (a), first write Carlos's marbles in terms of n, then double that amount for Dev. For (b), substitute n = 5 into each child's amount before adding.
Worked answer
- (a) Carlos = 9n − 3 marbles.
- (a) Dev = 2 × (9n − 3) = 18n − 6 marbles.
- (b) When n = 5: Hui Min = 45, Carlos = 42, Dev = 84.
- (b) Total = 45 + 42 + 84 = 171 marbles.
Answer: 171 marbles
The mistake this question tests
Habit
Calculation slip
Pupils often double only the 9n and forget to double the 3 subtracted, giving Dev 18n − 3 instead of 18n − 6.
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