# finding variance?

• Feb 17th 2010, 08:51 PM
sillylilly
finding variance?
heres the probability distribution table, it shows the number of tvs, n, sold per week:

N 1 2 3 4
P(N=n) 0.1 0.2 0.4 0.3

with the information, the fixed costs of the business which sells the tvs is \$900 per week and the profit per tv is \$375, find the variance in profit each week!
• Feb 18th 2010, 01:51 AM
mr fantastic
Quote:

Originally Posted by sillylilly
heres the probability distribution table, it shows the number of tvs, n, sold per week:

N 1 2 3 4
P(N=n) 0.1 0.2 0.4 0.3

with the information, the fixed costs of the business which sells the tvs is \$900 per week and the profit per tv is \$375, find the variance in profit each week!

Option 1: Construct a table for profit P and the associated probability. Note that P = 375N - 900. Then calculate variance from this table in the usual way.

Option 2: Calculate Var(N) from the given table and then calculate Var(P) = Var(375N - 900) = 375^2 Var(N).
• Feb 21st 2010, 01:32 PM
sillylilly
thanks, but.....