What is the value of S₁₂ + S₁₃ + S₁₄, where S_n is the sum of the first n natural numbers?
Answer and explanation
Correct answer: 274
Use the formula S_n = n(n + 1)/2 for the sum of the first n natural numbers. Thus S₁₂ = 12×13/2 = 78, S₁₃ = 13×14/2 = 91, and S₁₄ = 14×15/2 = 105. Their total is 78 + 91 + 105 = 274, so option A is correct. The original listed options and answer were inconsistent; they have been corrected here.
Frequently asked questions
What is the correct answer to this question?
274
Why is this the correct answer?
Use the formula S_n = n(n + 1)/2 for the sum of the first n natural numbers. Thus S₁₂ = 12×13/2 = 78, S₁₃ = 13×14/2 = 91, and S₁₄ = 14×15/2 = 105. Their total is 78 + 91 + 105 = 274, so option A is correct. The original listed options and answer were inconsistent; they have been corrected here.
Which subject and chapter does this question cover?
This is a Class 9 Mathematics question. Chapter: Sequences and Progressions. Topic: Sum of first n natural numbers.
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