Which number completes the pattern 1, 3, 6, 10, 15, 21, ___?

hard MCQ 3 marks Class 4 · Mathematics · Play with Patterns

Answer

B) 28

The correct answer is B) 28 — Therefore the correct option is $B) 28$ .

Step-by-step solution

Recognize the numbers as triangular numbers: $1, 3, 6, 10, 15, 21$ correspond to $T_{1}, T_{2}, T_{3}, T_{4}, T_{5}, T_{6}$ .
Triangular number formula: $T_{n} = n (n + 1) /2$ .
For the 6th term, $n = 6$ , giving $21$ .
The next term is the 7th triangular number: $T_{7} = 7 \times 8/2 = 28$ .
Therefore the correct option is $B) 28$ .

Common mistake: Confusing triangular numbers with square numbers

Concept tested: Triangular numbers