If the sum of the first (20) natural numbers is (210), what is the sum of the first (21) natural numbers?
Answer and explanation
Correct answer: 231
To obtain the sum of the first 21 natural numbers, add the next number, 21, to the sum of the first 20 numbers: \(S_{21}=S_{20}+21=210+21=231\). Hence, 231 is correct. The value 230 would result from adding 20, but the next natural number is 21. Exam tip: For consecutive sums, add the next term to the previous sum.
Frequently asked questions
What is the correct answer to this question?
231
Why is this the correct answer?
To obtain the sum of the first 21 natural numbers, add the next number, 21, to the sum of the first 20 numbers: \(S_{21}=S_{20}+21=210+21=231\). Hence, 231 is correct. The value 230 would result from adding 20, but the next natural number is 21. Exam tip: For consecutive sums, add the next term to the previous sum.
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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