Foundation June 2024 Paper 1 Q11
11 A window cleaner uses this formula.
| \(C = 2W + 5\) |
\(C\) = cost, in £, for the customer
\(W\) = number of windows to be cleaned
(a) How much does it cost for 6 windows to be cleaned? [2 marks]
(b) The cost for another customer was £24
Show why this cost must be incorrect. [1 mark]
| Answer | Mark | Comments |
|---|---|---|
| \(2 \times 6\) or 12 or 1700 | M1 | oe |
| 17(.00) | A1 | accept 1700p |
| Answer | Mark | Comments |
|---|---|---|
| 9.5 or \(9\frac{1}{2}\) or valid reason | B1 | eg shows that 9 windows cost £23 and 10 windows cost £25 or you can’t have half a window |
Additional guidance
| Calculated values must be correct | |
| (19, 21,) 23, 25 (, 27…) | B1 |
| Even number \(+\) 5 can’t be even / can’t end in a 4 | B1 |
| There’s no whole number you can times by 2 to get to 19 There’s no number you can times by 2 to get to 19 | B1 B0 |
| Even \(+\) 5 \(=\) odd, 24 is even Even \(+\) 5 \(=\) odd | B1 B0 |
| Costs are all always odd numbers, 24 is even Costs are all always odd numbers | B1 B0 |
| 19 is a prime number and so doesn’t divide exactly by 2 19 is a prime number | B1 B0 |