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Class 9MathematicsSequences and Progressionsnth termEasy
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In the sequence (1,3,6,10,\ldots), which term is (21)?

Answer and explanation

Correct answer: sixth term

Its rule is (a_n=\frac{n(n+1)}{2}), and (a_6=21). In exams, recognize the triangular-number pattern.

Related tags

SequencesProgressionsNth-TermClass-9EasyNth TermSequences And ProgressionsMathematics
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10 more MCQs
  1. 1In the sequence (1,4,9,16,...), what is the difference between the 15th term and the 14th term?
  2. 2What is the 25th term of the sequence (-5,-1,3,7,...)?
  3. 3If aₙ = n³ − n, what will be the value of a₇ − a₅?
  4. 4What will be the 12th term in the sequence (3, 5, 9, 15, 23, ...)?
  5. 5If a_n = n(n + 2), what will be the value of a_11 − a_8?
  6. 6If a_n = n^2 + 5n - 2, which term is equal to 148?
  7. 7The sequence (3, 8, 15, 24, …) has general term a_n = n² + 2n. Which term is 168?
  8. 8If a_n = n³ + n², what will be the value of a_6 − a_4?
  9. 9If a_n = 4n² − 1, which term is 575?
  10. 10In the sequence (1, 4, 9, 16, …), what will be the value of a_11 + a_12?
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