Higher November 2020 Paper 6 Q3
3 The graph shows the cost of electricity with Company A.
(a) Use the information in the graph to estimate the cost of electricity for a customer who uses 450 kwH of electricity. [3]
(b) Company B charges 14.3 pence per kwH of electricity used.
If Company B’s cost of electricity was plotted on the same axes as Company A’s cost of electricity, which line would be steeper?
Explain how you know. [3]
| Answer | Marks | Part marks and guidance | |
|---|---|---|---|
| 55.5[0] to 57.[0] nfww | 3 | M1 for 1 kwH costs £0.125 oe soi M1 for their 0.125 × 450 or cost × \(\frac{450}{\textit{their equivalent electricity use}}\) OR M1 for finding costs of electricity that sum to 450 kwH M1 for addition of these costs | eg 225 kwH costs £28.125 ± £0.5[0] 200 kwH costs £25 ± £0.5[0] 150 kwH costs £18.75 ± £0.5[0] 100 kwH costs £12.5 ± £0.5[0] 50 kwH costs £6.25 ± £0.5[0] eg \(25 \times \frac{450}{200}\) eg award M2 for 4 × (£12.5 ± £0.5[0]) + (£6.25 ± £0.5[0]) For the first M1 mark, costs must be from graph within ±½ small square ie ±£0.5[0] |
| Answer | Marks | Part marks and guidance | |
|---|---|---|---|
| Method 1: By performing a calculation for A and comparing with B: | Method 2: By performing a calculation for B and comparing with A: | ||
| 12.5 or 0.125 or “cost ÷ usage” using a reading from the graph or their (a) ÷ 450 | 1 | 14.3 × their chosen usage soi or [0].143 × their chosen usage soi May be implied by line on graph | Mark method not accuracy for first two marks e.g. 6.75 ÷ 50 = 0.135 but not 0.135 with no working |
| 14.3 or 0.143 stated or comparison against it clearly implied in a statement | 1dep | Cost in p or £ from graph for their chosen usage stated | Dep on first mark scored. Costs for A and B may be in different units. e.g. 1kwH costs 12.5p which is less than Company B’s charge |
| “B” with 12.5 and 14.3 or “B” with 0.125 and 0.143 or “B” with 12.5 or 0.125 and a comparison against 14.3 or 0.143 clearly implied | 1 | “B” with both costs correct and in same units | No follow through e.g. B because 1kwH costs 12.5p which is less than Company B’s charge |