Irrational numbers are numbers that can not be written as a simple fraction. An example of one would be
. Pi is about 3.14, but it goes on forever. You can not write pi as a simple fraction.
Answer:
68% of these phones last 3.87 years.
Step-by-step explanation:
Exponential distribution:
The exponential probability distribution, with mean m, is described by the following equation:

In which
is the decay parameter.
The probability that x is lower or equal to a is given by:

Which has the following solution:

The probability of finding a value higher than x is:

The average lifetime of a certain new cell phone is 3.4 years.
This means that 
So

68% of these phones last how long (in years)?
This is x for which:


Then






68% of these phones last 3.87 years.
The answer is letter c. x2-8x+24-[72/(x+3)]. If you do not know how to solve this using the long division method, you can always evaluate the options through the process of elimination first. Since the degree of the other factor is already 1 (x to the power of 1), you know that option d. is not the correct answer because you know that the other factor must be raised to the power of 2. That leaves us with a, b and c. Working backwards and multiplying the given factor (x+3) with the factor in b, gives us x3-5x2+72. So from there, you know that you have to eliminate 72, which can be removed when it is subtracted by itself. Letter c does just that. Try multiplying (x+3) and option c for yourself :).