Sequences
2 marks · EasyThe sequence 9, 12, 15, 18, ... is arithmetic. How many terms are there in the sequence up to and including 60?
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18 (±0.1)
Common mistakes: Forgetting to include the first term in count
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Marking points
M1 · 1 mark · Sets up and solves 9 + (n-1)×3 = 60
A1 · 1 mark · Correct value: n = 18
Worked solution
(n - 1) × 3 = 51
n - 1 = 17
n = 18