college algebra word problem

Question

Use the formula for the sum of the first n terms of the arithmetic sequence to find the sum.

5/2 +3+7/2+4+9/2

Answer 1

that's the same as 2 separate sums

(1/2)[5+7+9+11+ ...) and

3+4+5+6+ ....

Gaus' formula is (n/2)(n+1) for the sum of 1 through n

You'd have to subtract out though, 1 through 2 for the 2nd sum, so it would be

(n/2)(n+1) -3

then you need another formula for 1+3+ 5+7+9+ ... and also subtract out 1+3 or 4, also multiply by 1/2