In an AP the sum of the first 3 terms is ndash 60 and that of the last 3 are 84 If there are 15 term...........

Quantitative Aptitude ( CCS) Arithmetic progression

In an AP, the sum of the first 3 terms is – 60 and that of the last 3 are 84. If there are 15 terms, what is the sum of the middle 3 terms?

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Explanation:

Since the number of terms is odd,
the AP can be expressed as (a – 7d), (a – 6d), ---, a, ---, (a + 6d), (a + 7d).
The sum of the first 3 terms is (3a – 18d) = -60 and the sum of the last 3 terms is (3a + 18d) = 84.
Solving these two equations, we get a = 4 and d = 4.
Since the middle term is 4, the sum of the middle 3 terms is 12.