What is 2 times the difference between S_72 and S_36?
Answer and explanation
Correct answer: 3924
Apply S_n = n(n+1)/2. First, S_72 = 72 × 73/2 = 36 × 73 = 2628, and S_36 = 36 × 37/2 = 18 × 37 = 666. Their difference is 2628 − 666 = 1962. The question asks for twice this difference, so 2 × 1962 = 3924. Therefore option C is correct. A common mistake is to forget the final multiplication by 2, while the other nearby options can arise from an incorrect value of S_72, S_36, or a small subtraction error. Keeping the formula and the requested order clear avoids those mistakes.
Frequently asked questions
What is the correct answer to this question?
3924
Why is this the correct answer?
Apply S_n = n(n+1)/2. First, S_72 = 72 × 73/2 = 36 × 73 = 2628, and S_36 = 36 × 37/2 = 18 × 37 = 666. Their difference is 2628 − 666 = 1962. The question asks for twice this difference, so 2 × 1962 = 3924. Therefore option C is correct. A common mistake is to forget the final multiplication by 2, while the other nearby options can arise from an incorrect value of S_72, S_36, or a small subtraction error. Keeping the formula and the requested order clear avoids those mistakes.
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.
