What is the difference between the sum of the first (175) natural numbers and the sum of the first (125) natural numbers?
Answer and explanation
Correct answer: 7525
The sum of the first 175 natural numbers is \\(S_{175}=\frac{175\times176}{2}=15400\\), while the sum of the first 125 natural numbers is \\(S_{125}=\frac{125\times126}{2}=7875\\). Therefore, the difference is \\(15400-7875=7525\\). This is also the sum of the numbers from 126 to 175; 7475 results from an arithmetic error in subtraction. Exam tip: use \\(S_n=\frac{n(n+1)}{2}\\) for each sum and then subtract.
Frequently asked questions
What is the correct answer to this question?
7525
Why is this the correct answer?
The sum of the first 175 natural numbers is \\(S_{175}=\frac{175\times176}{2}=15400\\), while the sum of the first 125 natural numbers is \\(S_{125}=\frac{125\times126}{2}=7875\\). Therefore, the difference is \\(15400-7875=7525\\). This is also the sum of the numbers from 126 to 175; 7475 results from an arithmetic error in subtraction. Exam tip: use \\(S_n=\frac{n(n+1)}{2}\\) for each sum and then subtract.
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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