You could find S(9) - S(4) a = 5 and r = 2 S(9) = 5(2^9 - 1)/(2 - 1) = 2555 S(4) = 5(2^4 - 1)/(2 - 1) = 75 The terms from 5th to 9th add to 2555 - 75 = 2480
The other alternative method is the find the 5th term and add 5 terms starting from there T(5) = 5 x 2^(5 - 1) = 80 New sequence has a = 80 and r = 2 S(5) = 80(2^5 - 1)/(2 - 1) = 80 x 31 = 2480
