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Asked by  | 9th Mar, 2009, 11:47: AM

Expert Answer:

3 terms in the middle are 10th, 11th and 12th terms.

Hence, a+9d +a +10d +a + 11d = 129

⇒a+10d = 43  ...(1)

Last 3 terms are 19th, 20th and 21st terms

Hence, a+18d+a+19d+a+20d = 237

⇒a+19d = 79...(2)

Solving (1) and (2)

we get a = 3 and d=4

Hence, the AP is 3,7,11,15,19....83

 

Answered by  | 9th Mar, 2009, 02:33: PM

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