Answer:the answer is 3120
Answer:


Now we can find the expected value with this formula:

And replacing we got:

Step-by-step explanation:
For this case we know the following probability mass function given:

For this case we need to satisfy the following condition in order to have a probability distribution function:

And we have this:


Now we can find the expected value with this formula:

And replacing we got:

The denominator must be the same, so just think of the LEAST COMMON MULTIPLE, The LCM here is 8, because you can multiply 4 by 2 to get 8.
so when you multiply, you multiply both on the top and on the bottom, so this would be:
3 x 2 / 4 x 2 = 6 / 8
Now you can add or subtract: 6/8 - 1/8 = 5/8
Do them backwards and you will get the answer