# Tutor.com Probability Session

##### Apr. 13, 2012

Session Transcript - Math - Algebra II, 4/1/2012 8:46PM - Tutor.comSession Date: 4/1/2012 8:46PM
Length: 18.4 minute(s)
Subject: Math - Algebra II

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

Guest (Customer)
[00:00:03] A math teacher is randomly distributing 15 rulers with centimeter labels and 10 rulers without centimeter labels. What is the probability that the 1st ruler she hands out will have centimeter labels and the 2nd ruler will not have labels? On a certain day the chance of rain is 80% in SF and 30% in Sydney. Assume that the chance of rain in the two cities is independent. What is the probabilty that it will not rain in either city? A box contains 7 large red marbles, 5 large yellow marbles, 3 small red marbles, and 5 small yellow marbles. If a marble is drawn at random, what is the probabilty that it is yellow, given that it is one of the large marbles?

Allison P (Tutor)
[00:00:29] Welcome to Tutor.com ! I'm a little confused by what you put up. Is it more than one problem?

Guest (Customer)
[00:00:38] yes

Allison P (Tutor)
[00:01:40] Let's pick just one to put on the board to start.
[00:01:48] I'll let you choose.

Guest (Customer)
[00:01:57] can we do the first one

Allison P (Tutor)
[00:03:12] Did I get it all?

Guest (Customer)
[00:03:25] yes

Allison P (Tutor)
[00:04:36] Were you able to find a starting point or devise a method?

Guest (Customer)
[00:05:02] no

Allison P (Tutor)
[00:06:31] Can you tell me just the probability that she will hand our a ruler without centimeter labels?

Guest (Customer)
[00:06:55] what do u mean
[00:07:06] they just gave me those #

Allison P (Tutor)
[00:07:28] Have you worked with probability before?

Guest (Customer)
[00:07:35] not really

Allison P (Tutor)
[00:08:13] Probability is just the chance of something happening. The amount f what we are looking for over the total.

Guest (Customer)
[00:08:23] ok

Allison P (Tutor)
[00:09:01] The first choice she makes if for a ruler WITH CM. How many of those does she have?

Guest (Customer)
[00:09:28] 15

Allison P (Tutor)
[00:09:44] How many does she have total
[00:09:46] ?

Guest (Customer)
[00:10:22] don't know
[00:10:41] 25

Allison P (Tutor)
[00:11:00] You got it!

Guest (Customer)
[00:11:23] thats all

Allison P (Tutor)
[00:11:54] Now we have to consider the second choice. It gets multiplied by the first.
[00:12:05] How many DON'T have CM?

Guest (Customer)
[00:12:14] 10

Allison P (Tutor)
[00:13:12] How many total, remember she already picked one out.

Guest (Customer)
[00:13:45] 25

Allison P (Tutor)
[00:14:28] We took one out already so she only has 24 left.
[00:14:42] Does that make sense?

Guest (Customer)
[00:14:47] yes

Allison P (Tutor)
[00:15:10] Now we reduce these and multiply them together to get our answer.

Guest (Customer)
[00:15:58] correct

Allison P (Tutor)
[00:16:23] Almost, it is up until the last step. Try that again. 15/60 is right.
[00:17:09] 60/5 should be 12.
[00:18:01] Perfect!
[00:18:10] Do you have any questions about anything we went over today?