# Tutor.com Probabilities Session

##### Oct. 29, 2012

Session Transcript - Math - Statistics, 10/28/2012 7:14PM - Tutor.comSession Date: 10/28/2012 7:14PM
Length: 26.9 minute(s)
Subject: Math - Statistics

System Message
[00:00:00] *** Please note: All sessions are recorded for quality control. ***

Shakon (Customer)
[00:00:00] Need help on stats

Sara S (Tutor)
[00:00:11] Welcome to Tutor.com ! How can I help you today?

Shakon (Customer)
[00:01:24] With normal distribution
[00:01:32] meandistribution mean is .5
[00:01:39] standard d is .1
[00:01:56] p( x > .71)

Sara S (Tutor)
[00:02:42] I want to make sure that I am understanding the problem clearly. I'm going to put the information on the whiteboard. OK?

Shakon (Customer)
[00:03:14] Of course
[00:03:42] Yes that is what we need

Sara S (Tutor)
[00:03:52] Excellent! :)
[00:04:09] We have a formula for converting values to z-scores..
[00:04:14] Do you have that formula? :)

Shakon (Customer)
[00:04:50] Yes I do

Sara S (Tutor)
[00:05:11] Awesome!
[00:05:38] That is the correct formula! Let's ensure that we have all of the information that we need before plugging it into our formula.
[00:05:59] To find z.. we need an x value from the distribution, the mean (mu), and the standard deviation (sigma).
[00:06:04] Do we have those pieces?

Shakon (Customer)
[00:07:01] yes

Sara S (Tutor)
[00:07:26] Good! Would you mind plugging those pieces into the formula and calculating the zscore on the whiteboard? :)
[00:09:57] SUPER! :)
[00:10:23] So now we have a z score.. and with that value we can use our standard normal table (chart) to find probabilities..
[00:10:59] Do you have your normal table handy? :)

Shakon (Customer)
[00:11:51] Yes
[00:12:00] the answer is .0179

Sara S (Tutor)
[00:12:21] Awesome. You are good! :)
[00:12:24] Excellent!
[00:12:42] Do you have any questions over the material that we covered today? :)

Shakon (Customer)
[00:12:46] wait there
[00:12:56] there's another question
[00:12:57] included
[00:13:40] two hailstones picked up in a row will have diameters greater then .6 inch ?

Sara S (Tutor)
[00:13:44] Depending on the nature of the question, we may have time to go over an additional question... Would you please share the question?

Shakon (Customer)
[00:14:02] assume independence of the two diameters
[00:14:19] it is the same mean and standard deviation

Sara S (Tutor)
[00:14:48] Since we have finished the original question and there are students waiting, it would be best if you log back on and connect to another tutor to ask your next question.

Shakon (Customer)
[00:16:28] this is the second part to the same question
[00:16:30] :(

Sara S (Tutor)
[00:17:21] I can help you get started with the problem, but we may not have time to complete the problem in its entirety..

Shakon (Customer)
[00:17:30] okay.
[00:17:38] Just help me set it up
[00:17:45] i am completely lost
[00:17:46] :(

Sara S (Tutor)
[00:18:10] You'll set up the problem the same way that we set up the problem for x = 0.71..
[00:18:18] But instead, use 0.60.
[00:18:22] Does that make sense?
[00:18:24] :)
[00:19:15] Then once you have those probabilities calculated, you will use the rule of independent probabilities...

Shakon (Customer)
[00:19:20] but it says there are two hailstones :/

Sara S (Tutor)
[00:19:31] Do you remember some rules about independent events and calculating their probabilities?

Shakon (Customer)
[00:19:42] no
[00:19:52] oyr teacher didn't teach us

Sara S (Tutor)
[00:19:57] Correct, and the probability that one hailstone will be larger an 0.60 will be the same as another hailstone being larger an 0.60 if those two events are independent.

Shakon (Customer)
[00:20:21] doundo we times it at the end

Sara S (Tutor)
[00:21:10] The probability that two hailstones, assuming independence, will be larger than 0.60, you will use the formal multiplication rule.
[00:21:33] The formal multiplication rule states that the P(A and B) = P(A) *P(B).

Shakon (Customer)
[00:21:54] Can you show me on the board really quick then you can leave

Sara S (Tutor)
[00:22:42] The formula for the multiplication rule is on the whiteboard. :)
[00:23:15] Once you find your z score.. You calculated 1.00 as your z score. What is the associated probability for that score?

Shakon (Customer)
[00:23:10] So would we find the probability for one and
[00:23:15] timesand times it by two
[00:23:21] sincetwo since it is the same thing
[00:23:37] .8413

Sara S (Tutor)
[00:23:58] Almost.. :) Don't forget that you need to find the probability that it is GREATER than 0.60.
[00:24:04] Take it one more step. :)

Shakon (Customer)
[00:24:11] 1-.8413

Sara S (Tutor)
[00:24:18] Yes.

Shakon (Customer)
[00:24:17] =

Sara S (Tutor)
[00:24:20] :)

Shakon (Customer)
[00:24:37] .1587
[00:24:46] ???

Sara S (Tutor)
[00:24:56] A and B are the same event.. so once you find the probability, use that probability (0.1587) and multiply it by itself.
[00:25:03] P(A) = 0.1587
[00:25:08] P(B) = 0.1587

Shakon (Customer)
[00:25:07] oh by itself
[00:25:09] okat
[00:25:18] itself okay:) thank you so much <3

Sara S (Tutor)
[00:25:28] You did a great job today!

Shakon (Customer)
[00:25:26] you helped me so much

Sara S (Tutor)
[00:25:34] Do you have any questions about what we just did?
[00:25:42] :)

Shakon (Customer)
[00:25:50] npemuch pie.
[00:25:51] :)
[00:25:57] nope. :)

Sara S (Tutor)
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