SOLUTION: Use summation notation to express the sum. 5+20+80+......+20,971,520

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Question 880064: Use summation notation to express the sum.
5+20+80+......+20,971,520
Answer by richwmiller(17219) About Me  (Show Source):
You can put this solution on YOUR website!
Tn = t * r^(n - 1)
20,971,520 = 5 * 4^(n - 1)
20,971,520 = 5 * 4^(n - 1)
4194304=4^(n - 1)
n=12
S=t*(1 - r^n)/(1 - r)
S=5*(1 - 4^12)/(1 - 4)
S = 27962025