anonymous
  • anonymous
Consider a binomial random variable with n = 9 and p = 0.3. Let x be the number of successes in the sample. a. Find the probability that x is exactly 2. b. Find the probability that x is less than 2. c. Find P(x > 2). d. Find P(2 ≤ x ≤ 4). I've solved the a) but I can't get the other 3. I got 0.267 for a).
Mathematics
  • Stacey Warren - Expert brainly.com
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katieb
  • katieb
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anonymous
  • anonymous
For B, note that P(x < 2) = P(x = 0) + P(x = 1) since these are the only two values the random variable can take below 2.
anonymous
  • anonymous
So do i have to do the same thing i did for part a but repeat it for x = 0 and x = 1?
anonymous
  • anonymous
Yep, since you know how to calculate the probability the variable is equal to something you can use that to find the probability it is less than something.

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anonymous
  • anonymous
okay and for part c i do tht for x = 3 all the way up to 9? that would take forever...
anonymous
  • anonymous
For part C you can use the fact that P(x > 2) + P(x <= 2) = 1 and use your previous answers to calculate P(x > 2).
anonymous
  • anonymous
Otherwise you're right, it is a bunch of boring calculation :P
anonymous
  • anonymous
I dont understand
anonymous
  • anonymous
If something is not larger than 2, then that means it's less than or equal to 2. So P(x > 2) = 1 - P(x <= 2). From your first two answers you can calculate P(x <= 2) easily so that's why we do it this way.
anonymous
  • anonymous
Im sorry I still dont get it
anonymous
  • anonymous
That's ok, I'm just trying to think of ways to explain it :P Do you know that if you know the probability of something happening then the probability of it not happening is 1 minus that probability?
anonymous
  • anonymous
yeah
anonymous
  • anonymous
btw i think i solved part b is it 0.196?
anonymous
  • anonymous
It is :) So do you agree that P(x > 2) = 1 - P(x <= 2)?
anonymous
  • anonymous
I dont understand that formula
anonymous
  • anonymous
It comes from what I said above combined with the fact that is x is not > 2, then it is <= 2.
anonymous
  • anonymous
okay that makes sense
anonymous
  • anonymous
Alright. So can you find P(x <= 2)?
anonymous
  • anonymous
i did c9,1(0.3)^2(0.7)^9-1 and the same this for 0 to get 0.196
anonymous
  • anonymous
i used an online calculator to solve it because i dont know how to do it on my calclator
anonymous
  • anonymous
0.196 is P(x < 2), but you need P(x <= 2)
anonymous
  • anonymous
no part b says just less than 2 and i found out how to do it on my calculator had to use the nCr key
anonymous
  • anonymous
I mean for part C, since we know that P(x > 2) = 1 - P(x <= 2)
anonymous
  • anonymous
so would P(x <=2) be 0.267 + 0.196?
anonymous
  • anonymous
Yes. Then you can find the answer to C
anonymous
  • anonymous
so c would be 1 - (0.267+0.196)?
anonymous
  • anonymous
Yep!
anonymous
  • anonymous
Wow! thank you I actually understand what you were trying to say earlier
anonymous
  • anonymous
okay so how would i go about doing part d?
anonymous
  • anonymous
is it asking to find x = 3?
anonymous
  • anonymous
Well if 2 <= x <= 4 then that means x can be 2, 3, or 4.
anonymous
  • anonymous
right so how can i approach this?
anonymous
  • anonymous
would i have to solve for x = 2,3,4?
anonymous
  • anonymous
Yeah, I think the easiest way to do it here is to just calculate the probabilities for each case and sum them.
anonymous
  • anonymous
:( okay well atleast I know how to do these srot of questions thank you so much JE!
anonymous
  • anonymous
No worries, glad I could help! :)

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