How much will be the sum of natural numbers from (71) to (80)?
Answer and explanation
Correct answer: 755
There are 10 numbers from 71 to 80, inclusive. Using the sum formula for an arithmetic sequence:
\(\frac{10}{2}(71+80)=5\times151=755\).
Therefore, the correct answer is 755. A choice such as 745 may result from an error in counting the number of terms or finding the average. Exam tip: the number of terms from one endpoint to another is \(\text{last term}-\text{first term}+1\).
Frequently asked questions
What is the correct answer to this question?
755
Why is this the correct answer?
There are 10 numbers from 71 to 80, inclusive. Using the sum formula for an arithmetic sequence:
\(\frac{10}{2}(71+80)=5\times151=755\).
Therefore, the correct answer is 755. A choice such as 745 may result from an error in counting the number of terms or finding the average. Exam tip: the number of terms from one endpoint to another is \(\text{last term}-\text{first term}+1\).
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.
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