What is the difference between the sums of the first (90) and first (85) natural numbers?
Answer and explanation
Correct answer: 440
When the sum of the first 85 natural numbers is subtracted from the sum of the first 90 natural numbers, only the numbers from 86 to 90 remain. Thus, the difference is 86 + 87 + 88 + 89 + 90 = 440. Therefore, option C is correct. The value 450 would result from incorrectly treating each of the five terms as 90. Exam tip: In differences of such sums, cancel the common initial terms and add only the remaining consecutive terms.
Frequently asked questions
What is the correct answer to this question?
440
Why is this the correct answer?
When the sum of the first 85 natural numbers is subtracted from the sum of the first 90 natural numbers, only the numbers from 86 to 90 remain. Thus, the difference is 86 + 87 + 88 + 89 + 90 = 440. Therefore, option C is correct. The value 450 would result from incorrectly treating each of the five terms as 90. Exam tip: In differences of such sums, cancel the common initial terms and add only the remaining consecutive terms.
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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