Posted by Arun on Thursday, March 1, 2012 at 12:30am.
The probability that the life time of randomly chosen device is below average, average,above average are respectively 0.2,0.5,0.3. The probability that of the 3 randomly chosen devices lifetimes of 2 are above average and 1 below average equals
a.0.054,b.0.018,c.0.036,d.0.012

Probability and statistics  MathMate, Thursday, March 1, 2012 at 8:55am
Think of the expansion of the polynomial
(A+B+C)^3 where A=below, B=averave, C=above, and A+B+C=1.
1 is below average = A (0.2)
2 are above average = C (0.3)
term=AC^2
The coefficient of AC^2 is 3, i.e. 3AC^2.
The probability is therefore
3*0.2*0.3^2=0.054
Answer This Question
Related Questions
 Probability and statistics  5. The probabilities that the lifetime of a ...
 Maths  In a class of 75 students,15 are above average,45 are average and the ...
 Statistics  The average daily high temperatures in Lawton are approximately ...
 Statistics  An automatic machine in a manufacturing process is operating ...
 ap stats probability  over a 5 year period of time, 80% of winter days in ...
 math  Suppose the daily high temperature in a town is 3 degrees above average ...
 more statistics  The percent of fat calories that a person in America consumes ...
 statistics  Employees are evaluated as below average, average, or above average...
 Statistics  Use the following information to answer the following questions. IQ...
 Statistics  During September, the average temperature of Laurel Lake is 64.2ยบ ...
More Related Questions