Answer: C. 
Step-by-step explanation:
Given: Box contains 8 green balls and 4 purple balls.
Total balls = 8+4 = 12
event 1 = first picking green ball
event 2 = second picking purple balls.
As first ball was replaced, that means both events are independent.
Probability that you have selected a green ball and then a purple ball = P(purple ball )
Formula for probability = 
Probability of selecting a purple ball (second pick)= 

The required probability
, so C is correct option.
Exactly half of these integers are odd (1, 3, 5, ..., 29) so the probability of selecting an odd number is

.
Answer:

Step-by-step explanation:
The volume of a cylinder is given as:

Since the diameter is
, the radius is
.
Therefore, the volume of this cylinder is:
, using
as requested in the problem.
Since the tank is emptied at a constant rate of
, it will take
to empty the tank.
The two numbers are -18+ 2√(11) and -18 -2√(11).
-18+ 2√(11)+ [-18 -2√(11)]= -36
[-18+ 2√(11)]* [-18 -2√(11)]= 280.
Hope this helps~