Unit 4
6 marks · NormalA mobile phone contract offers a monthly price of £p, where p is calculated based on the formula p = 25 + 8n, with n the number of gigabytes of data used in a month.
A user receives a 20% discount on their total cost due to a special promotion.
Express the formula for p in terms of n.
Calculate the total price for a month if 6 GB of data are used.
Calculate the price the user will pay after the 20% discount.
Show how you calculated your answer to part (c).
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) p = 25 + 8n
(b) 73 £
(c) £58.40 £
(d) Discounted price = 73 × 0.8 = £58.40
Common mistakes: Deducting instead of multiplying by 0.8 for discount
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correct algebraic expression for p.
M1 (b) · 1 mark · Substitutes n = 6, p = 25 + 8×6 = 25 + 48 = 73
M2 (c) · 1 mark · Calculates 80% of total, i.e., multiplies by 0.8. (follow-through)
A1 (c) · 1 mark · Gives final answer £58.40. (follow-through)
E1 (d) · 2 marks · Clearly shows multiplying original price by 0.8 as discount calculation.
Worked solution
(a) p = 25 + 8n
(b) For n = 6: p = 25 + 8×6 = 25 + 48 = 73
(c) Price after 20% discount: 73 × 0.8 = £58.40
(d) Explanation: Multiply price by (1 − 0.2) = 0.8 to find discounted price.