My Math Forum Probability and standard deviation

 July 27th, 2013, 08:27 AM #1 Newbie   Joined: Jan 2013 Posts: 4 Thanks: 0 Probability and standard deviation Hi everyone please provide me the solution for the following problems on probability.Also please give me the valid and good explanation for the how you are arriving to the answers.Actually i am not finding good explanation for these problems in the book. Q1. The table below shows the distribution of a group of 40 college students by gender and class. Sex Sophomore Junior Senior ---------------------------------- M 6 10 2 F 10 9 3 ---------------------------------- If one student is selected from this group ,find the probability that the student chosen is female or sophomore. Q2. If an integer is read-only selected from all two 2-digit integer what is the probability that integer chosen has at least 4 in 10th place or unit place Q3) A random variable Y is normally distributed with a mean of 200 & a standard deviation of 10 Which one is greater I or II I Probability of the event that the value of Y is greater than 220 II 1/6 Thanks, Sagar.
 July 27th, 2013, 08:55 AM #2 Senior Member   Joined: Jun 2013 From: London, England Posts: 1,316 Thanks: 116 Re: Probability and standard deviation Here's what I would do with Q1. First, I'd try a simpler question. What is the probably that a student chosen at random is female? Well, there are 40 students and 22 of them are female, so the probability that one chosen at random is female is 22/40. I hope that makes sense. So, for Q1, you just have to count how many students meet the criteria of being female or sophomore. Well, you have the 22 females for a start. And, you also have 6 male sophomores. So, there are 28 who meet the criteria. So, the probability in this case is 28/40.

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