What is the difference between the sums of the first (75) and first (50) natural numbers?
Answer and explanation
Correct answer: 1575
The sum of the first \(n\) natural numbers is \(S_n=\frac{n(n+1)}{2}\). Thus, \(S_{75}=\frac{75\times76}{2}=2850\) and \(S_{50}=\frac{50\times51}{2}=1275\). Therefore, the difference is \(2850-1275=1575\). Although 1585 is close, it does not result from the correct subtraction. Exam tip: this difference can also be viewed as the sum of the numbers from \(51\) to \(75\).
Frequently asked questions
What is the correct answer to this question?
1575
Why is this the correct answer?
The sum of the first \(n\) natural numbers is \(S_n=\frac{n(n+1)}{2}\). Thus, \(S_{75}=\frac{75\times76}{2}=2850\) and \(S_{50}=\frac{50\times51}{2}=1275\). Therefore, the difference is \(2850-1275=1575\). Although 1585 is close, it does not result from the correct subtraction. Exam tip: this difference can also be viewed as the sum of the numbers from \(51\) to \(75\).
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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