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In the sequence 10, 20, 30, …, 200, which number is the 12th number?

hard 3 marks Class 2 · Mathematics · Counting in Tens

Answer

120

The correct answer is 120 — Compute $10 \times 12 = 120$ , so the 12th term is 120.

Step-by-step solution

Recognize the common difference is 10, so it is an arithmetic sequence.
Write the general term: $a_{n} = 10 \times n$ for $n g e 1$ .
Substitute $n = 12$ : $a_{12} = 10 \times 12$ .
Compute $10 \times 12 = 120$ , so the 12th term is 120.

Common mistake: Using

10 \times (12 - 1)

instead of

10 \times 12

Concept tested: Finding the nth term in a tens sequence

Published 10 October 2026 · How this solution was prepared and checked

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