Choose the correct sum of (1+2+3+\cdots+42).
Answer and explanation
Correct answer: 903
The sum of the first \(n\) natural numbers is \(\frac{n(n+1)}{2}\). Here, \(n=42\), so \(\frac{42\times43}{2}=21\times43=903\). Therefore, 903 is correct. The value 882 can result from incorrectly using \(42\times42/2\); the formula must include \(n+1=43\). Exam tip: Cancel the even number 42 with 2 before multiplying.
Frequently asked questions
What is the correct answer to this question?
903
Why is this the correct answer?
The sum of the first \(n\) natural numbers is \(\frac{n(n+1)}{2}\). Here, \(n=42\), so \(\frac{42\times43}{2}=21\times43=903\). Therefore, 903 is correct. The value 882 can result from incorrectly using \(42\times42/2\); the formula must include \(n+1=43\). Exam tip: Cancel the even number 42 with 2 before multiplying.
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.
