Question

The number of shooting stars in a particular region of the sky varies from night to night. Assume that the number of shooting stars (x) in that region has the following probability distribution:

x. 0. 1 2. 3

f(x) 0.80 0.15 0.04 0.01

What is the expected value for the number of shooting stars per night (to two decimal places)? Answer:

What is the standard deviation for the number of shooting stars per night (to three decimal places)? Answer:

Answer 1

Solution

x	P(x)	x * P(x)	x2 * P(x)
0	0.8	0	0
1	0.15	0.15	0.15
2	0.04	0.08	0.16
3	0.01	0.03	0.09
	1	0.26	0.4

Mean = = X * P(X) = 0.26

Standard deviation = =X 2 * P(X) - 2  

   =0.4 - 0.0676

=0.3324

= 0.5765

Standard deviation =0.576