probability and weather

[Xtian]

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the weatherman tells you there there is a 70% chance of rain each day for the next 3 days. what is the probability it will rain 2 out of the three days?...

 

[dvduplex]

3!/2!1! (.70)^2 (.30)^1 = .441

is that the correct answer?

 

[Xtian]

it is! Now how the heck did you know to use that equation?--I came up with 49/100. Please explain!!!

 

[dvduplex]

it is! Now how the heck did you know to use that equation?--I came up with 49/100. Please explain!!!

1) first, in order to get this: 3!/2!1!

3= the total number of days
2= number of days it will rain
1= number of days it will not rain

2) The probability of it will rain is 70% for 2 days. So, you will have to do this (.70)^2

3) The probability of it will not rain is 30% for 1 day. So, you will have to do this (.30)^1

4) Final step is to multiple everything.
3!/2!1! (.70)^2 (.30)^1

 

[Xtian]

awesome, thanks!