What is the ratio of the sum of the first (15) natural numbers to the sum of the first (10) natural numbers?
Answer and explanation
Correct answer: 24:11
The sum of the first \(n\) natural numbers is \(S_n=\frac{n(n+1)}{2}\). Thus, \(S_{15}=\frac{15\times16}{2}=120\) and \(S_{10}=\frac{10\times11}{2}=55\). Therefore, \(120:55=24:11\). Although \(11:5\) is close, it is not the simplified form of \(120:55\). Exam tip: always divide both terms of a ratio by their greatest common factor to simplify it.
Frequently asked questions
What is the correct answer to this question?
24:11
Why is this the correct answer?
The sum of the first \(n\) natural numbers is \(S_n=\frac{n(n+1)}{2}\). Thus, \(S_{15}=\frac{15\times16}{2}=120\) and \(S_{10}=\frac{10\times11}{2}=55\). Therefore, \(120:55=24:11\). Although \(11:5\) is close, it is not the simplified form of \(120:55\). Exam tip: always divide both terms of a ratio by their greatest common factor to simplify it.
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.
Student feedback
Was this question useful?
👍 0 Helpful 👎 0 Not helpful
Yes 0% No 0%
0 responsesStudent Reviews
No published reviews yet.
