CA Foundation · Quantitative Aptitude · Sequence and Series
The 5th term of an AP is 23 and its 12th term is 51. What is the 20th term of this AP?
The 20th term is 83. The difference between the 12th and 5th terms gives 7d = 28, so d = 4 and the first term is 7. Then the 20th term is 7 + 19×4 = 83.
- A79
- B83Correct
- C87
- D75
Explanation
Subtracting, 7d = 51 - 23 = 28, so d = 4. Then a = 23 - 4×4 = 7. The 20th term = 7 + 19×4 = 83. Check: 12th term = 7 + 44 = 51. Option 79 results from using 18 as the multiplier of d instead of 19.
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