Answer:
Step-by-step explanation:
+ At time 0 (beginning), the volume is 5 (feet^3) of sand.
+ After 1 minute, it lefts: 90% of 5 = 0.9*5
+ After 2 minutes, it left 90% of (0.9*5) = 0.9*(0.9*5)
or
[tex]5.(0.9)^{2}[/tex]
+ After 3 minutes, it left 90% of [tex]5.(0.9)^{2}[/tex]
or
[tex]5.(0.9)^{3}[/tex]
.......
+ After x minutes, it left 90% of [tex]5.(0.9)^{x-1}[/tex]
or
[tex]5.(0.9)^{x}[/tex]
So the answer is [tex]5.(0.9)^{x}[/tex], that means C
