Math  /  Data & Statistics

Questionv44(0.2)(0.8)v \sqrt{44(0.2)(0.8)}
10. Suppose the probability of a major earthquake on a given day is 1 out of 15,000 . Use the Poisson distribution to approximate the probability that there will be at least one major earthquake in the next 2000 days. poissun 1

Studdy Solution

STEP 1

What is this asking? What's the chance of at least *one* big earthquake happening in the next 2000 days, if the daily chance is super small? Watch out! We're approximating with the Poisson distribution, not calculating the exact probability!
Also, "at least one" is a sneaky way of asking about something else!

STEP 2

1. Calculate the average number of earthquakes.
2. Find the probability of *zero* earthquakes.
3. Calculate the probability of at least one earthquake.

STEP 3

We're given that the probability of an earthquake on any given day is 1/150001/15000.
We want to find the average number of earthquakes over 2000 days.
This is like saying, "If something happens 1/150001/15000 of the time, how many times do we expect it to happen in 2000 tries?"

STEP 4

To find the average number of earthquakes (λ\lambda), we **multiply** the **probability of an earthquake on a single day** by the **number of days**: λ=1150002000=200015000=215 \lambda = \frac{1}{15000} \cdot 2000 = \frac{2000}{15000} = \frac{2}{15} So, we expect an average of 215\frac{2}{15} earthquakes over 2000 days.
This makes sense, it's a small number because earthquakes are rare!

STEP 5

The Poisson distribution gives us the probability of *exactly* kk events happening, given an average rate of λ\lambda.
The formula is: P(k)=eλλkk! P(k) = \frac{e^{-\lambda} \cdot \lambda^k}{k!} We want to find the probability of *zero* earthquakes, so we'll plug in k=0k = 0.

STEP 6

Remember, λ\lambda is the average number of earthquakes we calculated earlier, which is 215\frac{2}{15}.
Also, 0!=10! = 1 and anything raised to the power of 0 is 1.
So, we have: P(0)=e215(215)00!=e21511=e215 P(0) = \frac{e^{-\frac{2}{15}} \cdot (\frac{2}{15})^0}{0!} = \frac{e^{-\frac{2}{15}} \cdot 1}{1} = e^{-\frac{2}{15}}

STEP 7

The probability of *at least one* earthquake is the same as 11 minus the probability of *no* earthquakes.
Think of it like this: all the possible outcomes add up to 1 (or 100%).
If we subtract the chance of *no* earthquakes, we're left with the chance of *one or more* earthquakes.

STEP 8

We just calculated the probability of zero earthquakes as e215e^{-\frac{2}{15}}.
Therefore, the probability of at least one earthquake is: P(at least one)=1P(0)=1e215 P(\text{at least one}) = 1 - P(0) = 1 - e^{-\frac{2}{15}}

STEP 9

The approximate probability of at least one major earthquake in the next 2000 days is 1e2151 - e^{-\frac{2}{15}}.

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