Foundation June 2017 Paper 2 Q15
15 Here are some numbers.
\[10 \qquad 13 \qquad 15 \qquad 20 \qquad 27 \qquad 39\]\(10 \qquad 15 \qquad 20 \qquad\) is an arithmetic progression.
Use three of the numbers to make a different arithmetic progression.
Describe the rule. [2 marks]
| Answer | Mark | Comments |
|---|---|---|
| 13 20 27 and Add 7 or 15 27 39 and Add 12 or 20 15 10 and Subtract 5 or 27 20 13 and Subtract 7 or 39 27 15 and Subtract 12 | B2 | oe rule B1 one correct arithmetic progression (using numbers from the list) with no or incorrect rule ie 13 20 27 or 15 27 39 or 20 15 10 or 27 20 13 or 39 27 15 |
Additional guidance
| Accept the expression for the \(n\)th term as the rule 13 20 27 and \(7n + 6\) or eg \(\times 7 + 6\) or 15 27 39 and \(12n + 3\) or 20 15 10 and \(25 - 5n\) or 27 20 13 and \(34 - 7n\) or 39 27 15 and \(51 - 12n\) | B2 |
| Ignore incorrect expression for the \(n\)th term alongside a correct rule eg 13 20 27 and Add 7 so \(n + 7\) | B2 |
| 13 20 27 and +7 or 7 more or going up in 7s | B2 |
| 20 15 10 and five times table (scores for the arithmetic progression) | B1 |
| 13 20 27 and \(n + 7\) (scores for the arithmetic progression) | B1 |
| Using number(s) not on the list | B0 |
| 10 15 20 and Add 5 | B0 |