Find the sum of the first (12) terms of the arithmetic progression (17,20,23,\ldots).
Answer and explanation
Correct answer: (402)
The governing concept is the sum of the first n terms of an arithmetic progression. The first term is a = 17 and the common difference is d = 20 − 17 = 3. The twelfth term is a₁₂ = a + 11d = 17 + 11 × 3 = 50. Applying Sₙ = n(a + l) ÷ 2 gives S₁₂ = 12(17 + 50) ÷ 2 = 6 × 67 = 402. Therefore, option B is correct. The multiplier 11 appears because reaching the twelfth term requires 12 − 1 differences. The other options can result from using an incorrect final term or from an arithmetic mistake in the formula.
Frequently asked questions
What is the correct answer to this question?
(402)
Why is this the correct answer?
The governing concept is the sum of the first n terms of an arithmetic progression. The first term is a = 17 and the common difference is d = 20 − 17 = 3. The twelfth term is a₁₂ = a + 11d = 17 + 11 × 3 = 50. Applying Sₙ = n(a + l) ÷ 2 gives S₁₂ = 12(17 + 50) ÷ 2 = 6 × 67 = 402. Therefore, option B is correct. The multiplier 11 appears because reaching the twelfth term requires 12 − 1 differences. The other options can result from using an incorrect final term or from an arithmetic mistake in the formula.
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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