Question

In a shipment of 18 trucks to a local truck dealer, there are six trucks that don't have air conditioning. Assume that you select four trucks at random.

What is the probability that two or fewer of the four don't have air conditioning?

Answer: ___________

Canada imports steel and exports automobiles. The value of unit of cars exported can be measured in in units of thousands of dollars per car per day by the random variable X. The random variable X has a mean of 4 and variance of 0.5. The value of the unit of steel imported is measured in units of thousands of dollars per ton of steel by the random variable Y. The random variable Y has a mean of 6 and variance of 2.4. Suppose that the country annually exports 10 cars and imports 5 tons of steel. The covariance between exports and imports is 0.2. The trade balance is defined as exports minus imports. The mean and variance of the trade balance is

A. 10 and 90, respectively

B. 12 and 80, respectively

C. 21 and 74, respectively

D. None of these answers are correct.

Answer 1

Solution:

   We are given that: In a shipment of 18 trucks to a local truck dealer, there are six trucks that don't have air conditioning.

Thus there are 18 - 6 = 12 trucks that have air conditioning.

four trucks are selected at random.

We have to find: the probability that two or fewer of the four don't have air conditioning.

let X = Number of trucks that don't have air conditioning

then

Let A = have air conditioning. and NA = Don't air conditioning.

then we have:

	NA	A
or	0	4
or	1	3
or	2	2

Thus we get:

where

similarluy we get: