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/sci/ - Science & Math

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4579801 No.4579801 [Reply] [Original]

Sorry guys, but I have no idea how to do this question. I'd appreciate someone helping me work through this.

Assume that 30% of all plants in a field are infested with aphids. Suppose that you pick 10 plants at random. What is the probability that none of them carried aphids?

Wouldn't we have to know the total amount of plants in the field?

>> No.4579804

Answer is apparently 0.028.

>> No.4579810
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4579810

But what if there are 10 plants in the field?

>> No.4579813

>Wouldn't we have to know the total amount of plants in the field?
lolwut
If you don't understand what you're doing wrong, perhaps you should finish high school before coming here.

>> No.4579820

Technically, you do have to know the number of plant, but I think the problem is assuming there's a really large number of plants. So the probability of one plant not having aphids is 0.7 and 0.7^10 ~ 0.028.

>> No.4579821

>>4579813

I'm in Calc 1, never taken Calc or probability in high school, so this is all new to me and this is the only question that has been stumped. I have a final in 1 hour, so give me a break.

>> No.4579822 [DELETED] 

<div class="math">0.7^10</div>

>> No.4579825

<div class="math">0.7^{10}</div>

>> No.4579829

>>4579825
>>4579820

What if it had asked what the probability that 2 of them carried aphids?

>> No.4579832

>>4579813
no he has a point


problem says 30% of plants in a field, not the probability of each is 30%. so as uou pick plants this changes

OP assume there are billions of plants in field and we can assume events are independent

>> No.4579836

>>4579829

Probability of the first two having aphids and the rest not, multiplied by the number of arrangements of 2 aphid carriers amongst 8 non-aphid carriers.

.3^2 * .7^8 * 10C2

>> No.4579834

>>4579829
then use the binomial distribution

>> No.4579837

>>4579829
>>4579829
It's a binomial probability distribution, so the probability that 2 carried asphids is
10C2 * 0.3^2 * 0.7^8

>> No.4579840

Do you have Binomial Theorem?
If so, it's 10Choose10 * .3^0 * .7^10
>>4579825
This post had it right, though simplified, but the same result. It's just the chance of picking an okay plant, 10 times.

And, as stated, this is assuming the events are independent, that is, there are enough plants that removing one has a negligable amount on the total.

>> No.4579849

>>4579829
(number of ways to choose two plants out of ten) * (the probability of those two having aphids) * (the probability the other eight don't)

10C2 * 0.3^2 * 0.7^8

>> No.4579857

Thanks a lot guys.

>> No.4579864

>>4579820
>>4579825
>>4579834
>>4579836
>>4579840
>>4579849
What are you doing guise?
Clearly, this is high school probability homework.
OP should pick up his book and look up the answer, or reread the text leading to the question.
Your not cool or smart for knowing such a simple thing.
You just gave faggots more reasons to start shitty hw threads.

>> No.4579876

>>4579864
I like hw threads