Multiple choice

Which term of the AP: 3, 8, 13, 18, _______ is 78?

  1. 15th term

  2. 16th term

  3. 17th term

  4. 14th term
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

 a = 3 and d = 5 (18 - 13, 13 - 8, 8 - 3 = 5) 78 = an = a + (n - 1)d 78 = 3 + (n - 1)5 78 = 3 + 5n - 5 $\Rightarrow$ 78 = 5n - 2 $\Rightarrow$ 78 + 2 = 5n 80 = 5n $\Rightarrow$ n = 16. So, 78 is the 16th term of the AP.

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