Moderate -0.8 This is a straightforward proof requiring students to factor n² + n = n(n+1) and recognize that consecutive integers always include one even number. It's simpler than average A-level questions as it only requires basic algebraic manipulation and a single conceptual insight about parity, typical of early proof questions in C1.
Question 9:
9 | n (n + 1) seen
= odd × even and/or even × odd
= even | M1
A1 | or B1 for n odd ⇒ n2 odd, and
comment eg odd + odd = even
B1 for n even⇒ n2 even, and
comment eg even + even = even
allow A1 for ‘any number
multiplied by the consecutive
number is even’ | 2