(scroll to bottom for answer)The equation you want to be using is A(n)+1=(A(n))r because this is a exponential sequence
r represents the ratio, which you said was 25, so basically you said
A(n)
____ = 25
A(n)-1
rthe sum of the first 2 terms are 16, the first two terms being A1 and A2, they need to follow the equation:
A2
__ = 25
A1
lets give them variables to make this a bit easier-
A1 will be x and A2 will be y
x+y=16(1st equation)
y/x=25, 25x=y(2nd equation)
(if you multiply y/x=25 by x you will get that 25x=y, which is where that other equation came from)
going back to x+y=16
subtract y from both sides
x=16-y
use substitution and solve for the second equation
25(16-y)=y
distribute
400-25y=y
add 25y to both sides to get rid of the -25y on the left side while keeping the equation equal
400=26y
divide both sides by 26 and you get 400/26 which simplifies to 200/13
after all that you need to multiply 200/13 by 25, 3 separate times
200 1875000
___ x 25 x 25 x 25= _________
13 13
pull it into a calculator and you get something like
142846.153846
