If an arithmetic progression has S₁₀ = 270 and S₅ = 85, what is the sum of the 6th to 10th terms?
Answer and explanation
Correct answer: 185
Let Sₙ denote the sum of the first n terms of the arithmetic progression. The sum of terms from the 6th through the 10th is obtained by removing the sum of the first five terms from the sum of the first ten terms. Thus, a₆ + a₇ + a₈ + a₉ + a₁₀ = S₁₀ − S₅ = 270 − 85 = 185. Therefore option C is correct. No separate calculation of the first or last term is needed. Options A, B, and D result from an incorrect subtraction or from confusing the requested five terms with another partial sum.
Frequently asked questions
What is the correct answer to this question?
185
Why is this the correct answer?
Let Sₙ denote the sum of the first n terms of the arithmetic progression. The sum of terms from the 6th through the 10th is obtained by removing the sum of the first five terms from the sum of the first ten terms. Thus, a₆ + a₇ + a₈ + a₉ + a₁₀ = S₁₀ − S₅ = 270 − 85 = 185. Therefore option C is correct. No separate calculation of the first or last term is needed. Options A, B, and D result from an incorrect subtraction or from confusing the requested five terms with another partial sum.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Arithmetic Progressions (AP). Topic: Finding the sum of the first $n$ terms of an AP.
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