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Class 9MathematicsSequences and ProgressionsSum of first n natural numbersMediumLevel 60
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What is the sum of the first (70) natural numbers?

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Answer and explanation

Correct answer: 2485

The sum of the first \(n\) natural numbers is \(\frac{n(n+1)}{2}\). Substituting \(n=70\), we get \(\frac{70\times71}{2}=35\times71=2485\). Therefore, 2485 is correct. A value such as 2475 results from an arithmetic error in multiplication or addition. Exam tip: cancel 2 with an even factor in \(n(n+1)\) before multiplying.

Related tags

MathematicsSequences And ProgressionsNatural NumbersSum FormulaArithmetic Series

Frequently asked questions

What is the correct answer to this question?

2485

Why is this the correct answer?

The sum of the first \(n\) natural numbers is \(\frac{n(n+1)}{2}\). Substituting \(n=70\), we get \(\frac{70\times71}{2}=35\times71=2485\). Therefore, 2485 is correct. A value such as 2475 results from an arithmetic error in multiplication or addition. Exam tip: cancel 2 with an even factor in \(n(n+1)\) before multiplying.

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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10 more MCQs
  1. 1Let A = {x : x is a natural number and x < 4}. What is A?
  2. 2If (a=10) and (d=2), what will be the sum of the first (6) terms?
  3. 3If a = 7 and d = 3, what is the sum of the first 6 terms?
  4. 4What is the sum of the first 6 terms of the arithmetic progression (15, 21, 27, 33, ...)?
  5. 5What is the sum of the first (10) natural numbers?
  6. 6Find the sum of the first (20) natural numbers.
  7. 7If \(S_n=\frac{n(n+1)}{2}\), what is \(S_{15}\)?
  8. 8What is the value of (1+2+3+\cdots+25)?
  9. 9Which is the sum of the first (30) natural numbers?
  10. 10How much is the sum of the first (12) natural numbers?
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