In a competition, (1) point is given for rank (1), (2) points for rank (2), and (13) points for rank (13). What is the total score?
Answer and explanation
Correct answer: 91
This is the sum of natural numbers from 1 to 13. Using \(1+2+\cdots+n=\frac{n(n+1)}{2}\), with \(n=13\), we get \(\frac{13\times14}{2}=91\). Hence, 91 is correct. Note that 78 is the sum from 1 to 12, so it is a close but incorrect option. Exam tip: identify the last term as \(n\) and apply \(\frac{n(n+1)}{2}\) directly.
Frequently asked questions
What is the correct answer to this question?
91
Why is this the correct answer?
This is the sum of natural numbers from 1 to 13. Using \(1+2+\cdots+n=\frac{n(n+1)}{2}\), with \(n=13\), we get \(\frac{13\times14}{2}=91\). Hence, 91 is correct. Note that 78 is the sum from 1 to 12, so it is a close but incorrect option. Exam tip: identify the last term as \(n\) and apply \(\frac{n(n+1)}{2}\) directly.
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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