What is the sum of (18+19+20+\cdots+36)?
Answer and explanation
Correct answer: 513
There are \(36-18+1=19\) terms from 18 to 36. Using the sum of an arithmetic progression, \(S=\frac{n}{2}(a+l)=\frac{19}{2}(18+36)=19\times27=513\). Hence, option A is correct. A value such as 523 results from using an incorrect number of terms or average. Exam tip: Always add \(+1\) when counting terms from one endpoint to another, inclusive.
Frequently asked questions
What is the correct answer to this question?
513
Why is this the correct answer?
There are \(36-18+1=19\) terms from 18 to 36. Using the sum of an arithmetic progression, \(S=\frac{n}{2}(a+l)=\frac{19}{2}(18+36)=19\times27=513\). Hence, option A is correct. A value such as 523 results from using an incorrect number of terms or average. Exam tip: Always add \(+1\) when counting terms from one endpoint to another, inclusive.
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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