Higher November 2018 Paper 3 Q8
8 Doug owes an amount of £600
He wants to pay off this amount in five months.
He says,
“Each month, I will pay back 20% of the amount I still owe.”
Show working to check if his method is correct. [3 marks]
| Answer | Mark | Comments |
|---|---|---|
| Alternative method 1 | ||
| \((600 \times)\ 0.8\) or 480 | M1 | oe |
| \(600 \times 0.8^2\) or 384 or \(600 \times 0.8^3\) or 307.2(0) or \(600 \times 0.8^4\) or 245.76 or \(600 \times 0.8^5\) or [196, 197] | M1dep | |
| [196, 197] and incorrect | A1 | oe eg 196.61 and no 196.61 still owed |
| Alternative method 2 | ||
| \(600 \times 0.2\) or 120 | M1 | oe |
| \(120 \times 0.8\) or 96 or \(96 \times 0.8\) or 76.8(0) or \(76.8(0) \times 0.8\) or 61.44 or \(61.44 \times 0.8\) or [49.15, 49.16] | M1dep | oe eg \((600 - 120) \times 0.2\) or \(480 \times 0.2\) |
| [403, 404] and incorrect | A1 | oe eg paid off 403.39(2) |
| Alternative method 3 | ||
| 0.8 | M1 | |
| \(0.8^5\) or 0.327 68 or 0.3277 or 0.328 or 0.33 | M1dep | |
| 0.327 68 (or 0.3277 or 0.328 or 0.33) and incorrect | A1 | oe |
Additional guidance
Ignore units
Full marks can be awarded for a correct explanation eg 120 and 96 calculated with a comment ‘as soon as the payment is below 120 a month it cannot be paid off in five months’