What is the sum of (71+72+73+\cdots+100)?
Answer and explanation
Correct answer: 2565
These are 30 consecutive natural numbers from 71 to 100. Therefore, their sum is \(\frac{30}{2}(71+100)=15\times171=2565\). Hence, option B is correct. A value such as 2535 can result from an error in counting the number of terms or finding the average. Exam tip: for consecutive numbers, first count the terms using \((\text{last}-\text{first}+1)\).
Frequently asked questions
What is the correct answer to this question?
2565
Why is this the correct answer?
These are 30 consecutive natural numbers from 71 to 100. Therefore, their sum is \(\frac{30}{2}(71+100)=15\times171=2565\). Hence, option B is correct. A value such as 2535 can result from an error in counting the number of terms or finding the average. Exam tip: for consecutive numbers, first count the terms using \((\text{last}-\text{first}+1)\).
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.
