What is the ratio of the sum of the first (25) natural numbers to the sum of the first (10) natural numbers?
Answer and explanation
Correct answer: 65:11
The sum of the first n natural numbers is \(S_n=\frac{n(n+1)}{2}\). Thus, \(S_{25}=\frac{25\times26}{2}=325\) and \(S_{10}=\frac{10\times11}{2}=55\). Therefore, the ratio is \(325:55=65:11\). Option 55:13 is incorrect because it is not obtained by simplifying 325:55 correctly. Exam tip: always reduce a ratio by dividing both terms by their greatest common factor.
Frequently asked questions
What is the correct answer to this question?
65:11
Why is this the correct answer?
The sum of the first n natural numbers is \(S_n=\frac{n(n+1)}{2}\). Thus, \(S_{25}=\frac{25\times26}{2}=325\) and \(S_{10}=\frac{10\times11}{2}=55\). Therefore, the ratio is \(325:55=65:11\). Option 55:13 is incorrect because it is not obtained by simplifying 325:55 correctly. Exam tip: always reduce a ratio by dividing both terms by their greatest common factor.
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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