Posted by **emi** on Saturday, June 7, 2014 at 2:30pm.

the sum of 11terms of A.P is 891.find the 28th and 45th terms if the common difference is 45

- math -
**Steve**, Saturday, June 7, 2014 at 4:26pm
If we add up terms n through n+10, then we get

(n+10)/2 (2a + (n+9)45) - (n-1)/2 (2a+(n-2)45) = 891

11a+495n = -1089

a+45n = -99

If we are adding up the first 11 terms, then a = -144 and

T28 = -144+27*45 = 1071

T45 = -144+44*45 = 1836

But, if we add up terms T5 through T15, then n=5, and a = -324 and

T28 = 891

T45 = 1656

Better tie down your conditions a bit better

## Answer This Question

## Related Questions

- Math - 1) If the sum of the first n terms of a series is Sn where Sn=2n²-n, (a)...
- math - 1) If the sum of the first n terms of a series is Sn where Sn=2n²-n, (a)...
- Math - An arithmetic progression has 10 terms. Sum of the 10 terms is 220. Sum ...
- Math - Sum of4th and the 6th terms of an a,p is 42 . While the sum of the 3rd ...
- Maths - The first term of an AP is 12 and that of a GP is 6. The common ...
- Math(arithmetic & Geometric Series) - 1)The sum of 6 terms of an arithmetic ...
- math - An arithmetic progression has 2 as its first term. find its common ...
- Math - The sum of the first and fourth terms of an arithimetic sequences is 2 ...
- Math - The first three terms of a GP are also the first,nineth and eleventh ...
- Maths - The 2nd, 5th, and 14th term Of an AP are consecutive terms of a GP. ...

More Related Questions