Probability of Rain Math Question

[JDawg1536]

If there is a 20% chance of rain today, 60% chance tomorrow, and 20% chance of rain in two days, what is the probability it will rain over the next three days? Anyone know how to figure that out? College stats seems like 20 years ago........

 

[ctbaars]

I don't know

 

[JDawg1536]

Haha, thanks. It shouldn't be hard, and it's bugging the hell out of me.

 

[frodrick]

1-(.8*.4*.8)=0.744 (74.4%) maybe?

 

[BlitzPuppet]

33%? Lol no idea.

 

[Printer Bandit]

42% or 9000%

 

[BoomerD]

Dood...20+60+20=100...there's a 100% chance of rain in the next 3 days!

 

[JDawg1536]

I think that's correct Frodrick. Thanks!

 

[Uppsala9496]

50%. It may rain. It may not.

 

[Phoenix86]

If there is a 20% chance of rain today, 60% chance tomorrow, and 20% chance of rain in two days, what is the probability it will rain over the next three days? Anyone know how to figure that out? College stats seems like 20 years ago........

% chance of rain has to do with % coverage for an area.

Re-worded, the question reads: If 20% of an area is covered with rain today, 60% is covered tomorrow, and 20% is covered the third day, what is the probability it will rain over the next 3 days.

The answer is 100%, ever day. Of course another acceptable answer is meteorologists are rarely accurate so you might as well flip a coin.

 

[DesiPower]

This is what I have seen over the years

20% = partly cloudy
30% = maybe it will drizzle somewhere in the town
40% = definitely will see some wet weather
50% or more = you will get some good rain

 

[edro]

Google and calculators are awesome, if you know how to use them.

http://www.calctool.org/CALC/math/probability/3_events

74.4% - Frod was right

 

[SP33Demon]

If there is a 20% chance of rain today, 60% chance tomorrow, and 20% chance of rain in two days, what is the probability it will rain over the next three days? Anyone know how to figure that out? College stats seems like 20 years ago........

.8*.4*.8= 25.6% chance it won't rain. 100-25.6 = 74.4% chance it will rain over those 3 days.

 

[Ricochet]

Dood...20+60+20=100...there's a 100% chance of rain in the next 3 days!

Seattle.

 

[JDawg1536]

Google and calculators are awesome, if you know how to use them.

http://www.calctool.org/CALC/math/probability/3_events

74.4% - Frod was right

Google?

 

[NoTine42]

The problem with chance of rain numbers in a forecast....those usually deal with the % of your listening / viewing area getting rain. While us mathematical types think it is talking about the odds our house will get rain.

The forecast over your house could be near 100% but an hour south of you will remain dry.

 

[BoomerD]

Seattle.

exactly

 

[Ferzerp]

Seattle "rain" isn't rain. It's like a drizzle or list misting.

 

[JDawg1536]

The problem with chance of rain numbers in a forecast....those usually deal with the % of your listening / viewing area getting rain. While us mathematical types think it is talking about the odds our house will get rain.

The forecast over your house could be near 100% but an hour south of you will remain dry.

Very true. I was just looking for the easy answer on calculating a problem like the one above, though.

 

[BoomerD]

Seattle "rain" isn't rain. It's like a drizzle or list misting.

Well...I live a short distance away from Seattle. We've had about 1.75" of "drizzle" in the past 24 hours...:whiste:

 

[edro]

Google?

Search for: probability calculator 3 events

 

[Ferzerp]

Well...I live a short distance away from Seattle. We've had about 1.75" of "drizzle" in the past 24 hours...:whiste:

That you think under 2" of rain in 24 hours is notable sort of illustrates my point. Seattle rainfall per year is only about 37"

 

[e-ricesucks]

depends where you are
10 more posts for pm

 

[BarkingGhostar]

I think the way they express things and how they are interpreted by the unwashed masses (dirty fuckers) is that 20% chance of rain means for a given set of conditions assumed for the day in question the last five exact days of those conditions had one day rain.

So, for the next five days in the future where they forecast 20% chance of rain you can think of one of them getting the ground wet.

 

[mmntech]

Here's a wrench in the system. I learned from a meteorologist some time ago that forecast accuracy drops by 15% per day.