A staircase has layers of (1), (2), (3) bricks up to (10) bricks. How many bricks are there in total?
Answer and explanation
Correct answer: 55
The number of bricks in the layers runs from 1 to 10, so the total is \(1+2+3+\cdots+10\). The sum of the first \(n\) natural numbers is \(\frac{n(n+1)}{2}\). Thus, \(\frac{10\times11}{2}=55\), so 55 is correct. The value 45 is the sum from 1 to 9, making it a close but incorrect option. Exam tip: for the sum from 1 to \(n\), use \(\frac{n(n+1)}{2}\) directly.
Frequently asked questions
What is the correct answer to this question?
55
Why is this the correct answer?
The number of bricks in the layers runs from 1 to 10, so the total is \(1+2+3+\cdots+10\). The sum of the first \(n\) natural numbers is \(\frac{n(n+1)}{2}\). Thus, \(\frac{10\times11}{2}=55\), so 55 is correct. The value 45 is the sum from 1 to 9, making it a close but incorrect option. Exam tip: for the sum from 1 to \(n\), use \(\frac{n(n+1)}{2}\) directly.
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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