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Algebra · form and evaluate expressions
P6 · Algebra · PSLE Maths
Question
Mei Ling bought 4 meal coupons at $n each and 3 drink coupons at $2 each for a school carnival. She used a $5 voucher. (a) Write an expression, in terms of n, for the amount she paid. (b) If n = 3.50, how much did she pay?
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Hint
Translate each phrase into maths: 4 coupons at $n each is 4n; 3 coupons at $2 each is 3 × 2; a voucher means subtract $5.
Show the answer and step-by-step explanation
Answer: Expression for amount paid 4n+1; Amount paid when n = 3.50 15 $
- Find the unknown — Each meal coupon costs $n. She buys 4 of them, so 4 meal coupons cost 4n dollars.
- Add drink coupons — There are 3 drink coupons at $2 each: 3 × 2 = 6, so the drink coupons cost $6 altogether.
- Write cost first — The 4 meal coupons cost 4n, and the drink coupons cost 6. Before using the voucher, the total is 4n + 6.
- Subtract voucher — Using a $5 voucher means we subtract 5 from the total. So the expression for the amount paid is (4n + 6) − 5 = 4n + 1.
- Substitute n — Now substitute n = 3.50 into the expression 4n + 1.
- Write answer — So the expression for the amount paid is 4n + 1. When n = 3.50, the amount paid is $15. 📌 Key idea: when you see “$n each, buy some”, write “some n”; subtract vouchers or discounts; then substitute the value of n.
Method: Translate the words step by step into an algebraic expression: unit cost × quantity; add extra costs; subtract vouchers or discounts. Then substitute the value of n and evaluate.
Practice: 3 similar questions
- Ali bought 6 badges at $n each and paid $4 for postage. (a) Write an expression, in terms of n, for the total cost. (b) If n = 2.50, what was the total cost?
Answer
0, 19 $ — 6 badges at $n each cost 6n. Add the $4 postage, so the total cost is 6n + 4. Substitute n = 2.50: 6 × 2.50 + 4 = 15 + 4 = 19.
- Raju bought 5 science files at $n each and 2 pens at $1.80 each. He used a $3 voucher. (a) Write an expression, in terms of n, for the amount he paid. (b) If n = 2.40, how much did he pay?
Answer
0, 12.60 $ — 5 files at $n each cost 5n. Cost of 2 pens: 2 × 1.80 = 3.60. Using the $3 voucher: 5n + 3.60 − 3 = 5n + 0.60. Substitute n = 2.40: 5 × 2.40 + 0.60 = 12 + 0.60 = 12.60.
- Siti and 3 friends bought 8 movie tickets at $n each. They used a $12 group voucher and shared the remaining cost equally among 4 people. (a) Write an expression, in terms of n, for the amount each person paid. (b) If n = 9.50, how much did each person pay?
Answer
0, 16 $ — 8 tickets at $n each cost 8n. After using the $12 voucher, the remaining cost is 8n − 12. Share equally among 4 people: (8n − 12) ÷ 4 = 2n − 3. Substitute n = 9.50: 2 × 9.50 − 3 = 19 − 3 = 16.
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