How much is the sum of natural numbers from (81) to (90)?
Answer and explanation
Correct answer: 855
There are \(10\) numbers from 81 to 90. Their average is \(\frac{81+90}{2}=85.5\), so the sum is \(10\times 85.5=855\). Hence, option B is correct. A value such as \(845\) can result from an error in counting the terms or finding the average. Exam tip: for consecutive numbers, use \(\text{number of terms}\times\text{average of the first and last terms}\).
Frequently asked questions
What is the correct answer to this question?
855
Why is this the correct answer?
There are \(10\) numbers from 81 to 90. Their average is \(\frac{81+90}{2}=85.5\), so the sum is \(10\times 85.5=855\). Hence, option B is correct. A value such as \(845\) can result from an error in counting the terms or finding the average. Exam tip: for consecutive numbers, use \(\text{number of terms}\times\text{average of the first and last terms}\).
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.
Student feedback
Was this question useful?
👍 0 Helpful 👎 0 Not helpful
Yes 0% No 0%
0 responsesStudent Reviews
No published reviews yet.
