# Elementary Statistics Question

• May 16th 2010, 10:04 AM
statisticsStudent
Elementary Statistics Question
I'm taking a college level math course but it is "elementary stats" so it's intro level. Anyway, I am always nervous about the homework questions because I'm afraid I'll get them wrong or that I'm misinterpreting them, and one of the questions due for homework has me stumped. We've been studying random variables and probability distributions and I thought I got it but the question is just so vague I can't really figure out what the values for X and the values for P(X) are supposed to be. THe question runs: "Two dice are rolled. Let the random variable X denote the sum of the two numbers obtained. Construct the probability histogram for the random variable X." I understand how to do probability histograms, with the probabilities on the vertical axis and the values along the horizontal axis, but I"m not sure what the values and probabilities would be in this case? All I've been able to come up with is that if you roll 2 dice, the total number of possible outcomes would be 6x6= 36. I'm not sure where to go from there?
• May 16th 2010, 12:47 PM
rubic
Let the random variable X denote the sum of the two numbers obtained.
X can take values between 2 to 12,
P(x=2) = there is only one option first die 1 and second die 1= 1/6*1/6 =1/36
P(x=3) = now there are two options (1,2),(2,1) = 2*(1/6*1/6) = 2/36
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hint
1)total probability = 1
2)draw 6x6 diagram for the sum, to see number of different possibilities for X=x

hope it helps