Answer:
Population of bacteria at time
is 
Step-by-step explanation:
The complete question is
If
represents the number of bacteria in a culture at time t, how many will there be at time 
Solution
Given
The population of bacteria after time t is equal to 
Population when at time 
We will substitute the value of time in above equation.

Answer:
I have no idea if this would be right but I am guessing (for the 1/5 one) if you put 5 different colored marbles in a container and wanted to pull out a red one. You can also do this for the 1/10 one just use a different object.
Step-by-step explanation:
-5x = 10 + 10
-5x = 20
X = 20/-5
X = -4
check :
-5 x -4 =20
20 =20