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Mathematics

Which term of the A.P. 21, 42, 63, 84, … is 210?

  1. 9th

  2. 10th

  3. 11th

  4. 12th

AP GP

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Answer

Here, a = 21, d = 42 - 21 = 21.

Let nth term be 210, so an = 210.

We know that

    an = a + (n - 1)d
∴ 210 = 21 + (n - 1) × 21
⇒ 210 = 21 + 21n - 21
⇒ 21n = 210
⇒ n = 10

Hence, Option 2 is the correct option.

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