Posted by **raksha** on Sunday, October 28, 2007 at 12:38am.

Suppose that the time (in hours) required to repair a machine is an exponentially distributed random variable with parameter λ (lambda) = 0.5.

What's the probability that a repair takes less than 5 hours? AND what's the conditional probability that a repair takes at least 11 hours, given that it takes more than 8 hours?

- math -
**drwls**, Sunday, October 28, 2007 at 1:21am
The probability distribution you are talking about is

f (x; lambda) = lambda exp^-(lambda x), x > 0

It is discussed at http://en.wikipedia.org/wiki/Exponential_distribution

The probability that a repair takes less than x is

F (x; lambda) = 1 - exp(-lambda x)

For x = 1 - exp(-2.5) = 0.918

The fraction taking 8 hours or more to repair is

exp(-4) = 0.01832

The fraction taking 11 hours to repair is

exp(-5.5) = 0.00409

That means that 409/1832 = 22% of the repairs taking 8 hours or more require more than 11 hours.

## Answer This Question

## Related Questions

- intro to probability - For the sheet-metal stamping machine in a certain factory...
- probability - Let K be a discrete random variable with PMF pK(k)=⎧⎩...
- probability - The lifetime of a type-A bulb is exponentially distributed with ...
- statistics - The duration of time it takes General Motors to build a car is ...
- probability - Suppose that you have two laptops, both of which you begin using ...
- Probability - Suppose that you have two laptops, both of which you begin using ...
- Probability - Caleb builds a particle detector and uses it to measure radiation ...
- statistics - A manufacturer of luxury SUVs is concerned because warranty claims ...
- Algebra - A furnace repair service charged a customer $80 for parts and $65 per ...
- probability - lengths of the different pieces are independent, and the length of...

More Related Questions