June 2025 Paper 3 Q7
7 Solve the equation
\[\sum_{r=1}^{3} (ar + 5) = 57\]to find the value of \(a\) [3 marks]
| Scheme | Marks | AO |
|---|---|---|
| Obtains \(a + 5\), \(2a + 5\) and \(3a + 5\) PI by correct answer or \(6a + 15\) ACF | B1 | 2.5 |
| Forms an equation using sum of three terms with at least two of \(a + 5\), \(2a + 5\) or \(3a + 5\) or uses \(S_n = \dfrac{n}{2}\left(2a + (n - 1)d\right)\) with at least two of \(n = 3\), first term \(a + 5\) and \(d = a\) or uses \(S_n = \dfrac{n}{2}(a + L)\) with at least two of \(n = 3\), first term \(a + 5\) and \(L = 3a + 5\) or uses \(6a + 15\) in an equation Must use 57 in the equation PI by correct answer | M1 | 3.1a |
| Obtains 7 | A1 | 1.1b |
| (3 marks) |