stat guys - - need some help here (1 Viewer)

gameday · Jan 28, 2015

I think I know the answer to this, but I'm not sure.

Here is a scenario:

1) there is a 25% chance it'll rain in WI

2) there is a 25% chance it'll rain in CA

3) there is a 25% chance it'll rain in NY

What is the probability that it will rain in at least 1 of those states?

A guy is trying to convince me it is 75%. Since these are completely independent events I believe it is 25%.

Help me out here. TIA.

ChiefD · Jan 28, 2015

Sleep with his wife 100% of the time.

bryhamm · Jan 28, 2015

gameday said:
I think I know the answer to this, but I'm not sure.

Here is a scenario:

1) there is a 25% chance it'll rain in WI

2) there is a 25% chance it'll rain in CA

3) there is a 25% chance it'll rain in NY

What is the probability that it will rain in at least 1 of those states?

A guy is trying to convince me it is 75%. Since these are completely independent events I believe it is 25%.

Help me out here. TIA.

so to him, if you include a 4th state that has a 25% chance of rain then there will be a 100% chance that it would rain in at least one state? lol

ask him what happens when you include a 5th state with a 25% chance of rain.

Gawain · Jan 28, 2015

1-(3/4*3/4*3/4) or 37/64 or 57.8%

mr roboto · Jan 28, 2015

bryhamm said:
gameday said:

I think I know the answer to this, but I'm not sure.

Here is a scenario:

1) there is a 25% chance it'll rain in WI

2) there is a 25% chance it'll rain in CA

3) there is a 25% chance it'll rain in NY

What is the probability that it will rain in at least 1 of those states?

A guy is trying to convince me it is 75%. Since these are completely independent events I believe it is 25%.

Help me out here. TIA.

Click to expand...

so to him, if you include a 4th state that has a 25% chance of rain then there will be a 100% chance that it would rain in at least one state? lol

ask him what happens when you include a 5th state with a 25% chance of rain.

gianmarco · Jan 28, 2015

Gawain said:
1-(3/4*3/4*3/4) or 37/64 or 57.8%

This.

Easier way to think of it is "what are the chances it will not rain in each of those states". So you have a 3/4th chance in each of those states. Thus, it's easier to think of the chance of it not raining in all 3 states is 3/4 * 3/4 * 3/4 or 42.2%. The remainder, 57.8%, is the chance it will rain in at least one of the states.

Brony · Jan 28, 2015

http://en.wikipedia.org/wiki/Complementary_event

dgreen · Jan 28, 2015

bryhamm said:
gameday said:

I think I know the answer to this, but I'm not sure.

Here is a scenario:

1) there is a 25% chance it'll rain in WI

2) there is a 25% chance it'll rain in CA

3) there is a 25% chance it'll rain in NY

What is the probability that it will rain in at least 1 of those states?

A guy is trying to convince me it is 75%. Since these are completely independent events I believe it is 25%.

Help me out here. TIA.

Click to expand...

so to him, if you include a 4th state that has a 25% chance of rain then there will be a 100% chance that it would rain in at least one state? lol

ask him what happens when you include a 5th state with a 25% chance of rain.

Yeah, that's a nice way to show why 75% doesn't make sense, but 25% doesn't make sense either. As you suggest, let's just keep adding states (or even removing states). If 50 states each had a 25% chance, it doesn't make sense to think that there's only a 25% chance that at least 1 gets rain. It's clear that the answer is 25% if there's only one state. But, each time you add a state, you are increasing the chances that it rains in at least one state. If 1,000,000 geographic regions each have a 25% chance, it's going to be really close to a 100% chance that it rains in at least one of them.

Same with the lottery. We may know that each individual has a 0.00001% (totally made up a number here) chance of winning, but we wouldn't say that there's a 0.00001% chance that at least one person wins. We understand that someone will probably win.

Leroy Hoard · Jan 28, 2015

ChiefD said:
Sleep with his wife 100% of the time.

Closest I came was 75%.

gameday · Jan 28, 2015

Thanks for the answers. I get it now.

Ignoramus · Jan 28, 2015

gameday said:
I think I know the answer to this, but I'm not sure.

Here is a scenario:

1) there is a 25% chance it'll rain in WI

2) there is a 25% chance it'll rain in CA

3) there is a 25% chance it'll rain in NY

What is the probability that it will rain in at least 1 of those states?

A guy is trying to convince me it is 75%. Since these are completely independent events I believe it is 25%.

Help me out here. TIA.

There's a 50% probability that the forecast will be correct.I wish I had a job where I could be wrong that much and still be employed, amirite!?!

Cjw_55106 · Jan 28, 2015

Let's put it this way:

If two guys are having a discussion that neither of them have a clue about, what are the chances either of them will be right? I don't have the stats to back it up, but current evidence suggests 100% chance they will both be wrong.

brun · Jan 28, 2015

Gawain said:
1-(3/4*3/4*3/4) or 37/64 or 57.8%

This, or 100% if I've got a tee time scheduled in one of those places.

belljr · Jan 28, 2015

Gawain said:
1-(3/4*3/4*3/4) or 37/64 or 57.8%

but there's 50 states

SoBeDad · Jan 28, 2015

belljr said:
Gawain said:

1-(3/4*3/4*3/4) or 37/64 or 57.8%

Click to expand...

but there's 50 states

Use the Binomial Probability calculator to find many this and many related probabilities. Probability of rain in at least 1 of 50 states, given a 25% chance in each state: 0.999999433678344.

Probability of rain in at least 15 of 50 states: 0.251918855477241; in at least 25 states: 0.000122513451651041. And so on.

belljr · Jan 28, 2015

SoBeDad said:
belljr said:

Gawain said:

1-(3/4*3/4*3/4) or 37/64 or 57.8%

Click to expand...

but there's 50 states

Click to expand...

Use the Binomial Probability calculator to find many this and many related probabilities. Probability of rain in at least 1 of 50 states, given a 25% chance in each state: 0.999999433678344.Probability of rain in at least 15 of 50 states: 0.251918855477241; in at least 25 states: 0.000122513451651041. And so on.

but it has to be those one of those not any 3 states.

dancer · Jan 29, 2015

gameday said:
Since these are completely independent events

You are stating this as a known...if this is true than the 57.8% stated here is correct.

But is this a fact?

I guess the three states are far enough apart that you probably won't have one storm that can cause rain in multiple places (if you could, this positive correlation would decrease the 57.8% to something smaller).

But could be that weather patterns are such that, for example, if it doesn't rain in CA it is then more likely to rain in WI...if there is such negative correlation, the probability is higher than 57.8%.

Need to get all of the correlations to get a precise answer...

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stat guys - - need some help here (1 Viewer)

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