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 - An automatic machine in a manufacturing process is operating ...
- more statistics - The percent of fat calories that a person in America consumes ...
- COLLEGE MATH - In 2003, the probability that a randomly chosen bag of cement ...
- MATH - (4 pts) The score on an exam from a certain MAT 112 class, X, is normally...
- ap stats-- probability - over a 5 year period of time, 80% of winter days in ...
- stat - Problem 2. THE PROBABILITY THAT A RANDOMLY CHOSEN SALES PROSPECT WILL ...
- Statistics - During September, the average temperature of Laurel Lake is 64.2º ...
- stats - The percent of fat calories that a person that in America consumes each ...