Posted by **Abdela** on Thursday, February 16, 2012 at 6:54am.

The sum of the first 5 terms of an arthmetic sequence, is 30 and the sum of the next 4 terms is 69 .

Find the arthemetic progression?

- Math sequence -
**Reiny**, Thursday, February 16, 2012 at 8:43am
so the sum of the first 9 terms would be 99

sum(5) = 30 ---> (5/2)(2a + 4d) = 30

5(2a+4d) = 60

2a + 4d = 12

a + 2d = 6

sum(9) = 99 ----> (9/2)(2a + 8d) = 99

2a + 8d = 22

a + 4d = 11

subtract them

2d = 5

d = 5/2 or 2.5

then a = 1

the arithmetic sequence is

1 , 3.5, 6, 8.5 , ...

- Math sequence -
**Abubakar1idr**, Thursday, February 16, 2012 at 2:26pm
What is lhe sum of lhe first 12 terms of an A.p whose first term is 15 and common difference is 13.

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