Multiple choice

Which term of the given series in AP is 78? 3, 8, 13, 18, …

  1. 15th

  2. 16th

  3. 17th

  4. 18th
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B Correct answer
Explanation

AP: 3, 8, 13, 18... a=3, d=5. an = a + (n-1)d. 78 = 3 + (n-1)5 => 75 = (n-1)5 => 15 = n-1 => n = 16.

AI explanation

Using the formula for the nth term of an arithmetic progression, a_n = a + (n - 1)d, where a is 3 and d is 5. We set the equation to 78, resulting in 78 = 3 + (n - 1)5. Solving for n, we get 75 = (n - 1)5, which simplifies to 15 = n - 1, making n = 16.

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