algebra help need formula for sum?

Question

day 1=5,day2=10,day 3=20,d4=40,d5=80,d6=160,d7=320,d8=640 etc..

Answer 1

With the info you provided, it's clear that as you move from one day to the next, the value doubles.

KEY is that you'll need a variable to represent the day you're calculating.

Let's say we use Dt to represent today's value and Dy to mean yesterday's value.

Today's value is equal to double yesterday's value, which mathematically translates to:

Dt = Dy x 2 = 2Dy

So if Dy = 6, then Dt would = 2 x 6 = 12.

Answer 2

D=1 to D summation

2(x(D-1))

x(0)=5

Answer 3

Dn-1*2