How much is the sum of natural numbers from (211) to (260)?
Answer and explanation
Correct answer: 11775
There are 50 terms from 211 to 260, inclusive. Using the arithmetic progression sum formula, \(S=\frac{n}{2}(\text{first term}+\text{last term})\), we get \(S=\frac{50}{2}(211+260)=25\times471=11775\). Hence, option B is correct. A nearby value such as 11675 may result from counting the number of terms incorrectly. Exam tip: when both endpoints are included, use \(\text{last}-\text{first}+1\) for the number of terms.
Frequently asked questions
What is the correct answer to this question?
11775
Why is this the correct answer?
There are 50 terms from 211 to 260, inclusive. Using the arithmetic progression sum formula, \(S=\frac{n}{2}(\text{first term}+\text{last term})\), we get \(S=\frac{50}{2}(211+260)=25\times471=11775\). Hence, option B is correct. A nearby value such as 11675 may result from counting the number of terms incorrectly. Exam tip: when both endpoints are included, use \(\text{last}-\text{first}+1\) for the number of terms.
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.
