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Probability My poor English 
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#1
May512, 09:12 PM

P: 963

Find the probability of scoring a total of 7 points (a) once, (b) at least once, (c) twice, in 2 tosses of a pair of dice.
My question. 1. What does scoring a total of 7 points mean? Is it 1+6 or 2+5 or 3+4 or 4+3 or 5+2 or 6+1 2. Is in 2 tosses of a pair of dice means that throwing 2 dices at once twice. How this relate to scoring of 7 points. Thank you. 


#2
May512, 09:15 PM

P: 606




#3
May612, 03:57 PM

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P: 39,293

Because you say specifically "2 tosses of a pair of dice" the reference is to rolling a pair of dice two different times. Each time you roll a pair of dice you can get any number from 1 to 6 (all equally likely) on the first die and 1 to 6 (all equally likely) on the second die. That means that there are 6x6= 36 equally likely combinations of two dice. Of course, the number they add to aren't equally likely. Only (1, 1) gives a sum of 2, only (6, 6) adds to 12, while (1, 6), (2, 5), (3, 4), (4, 3), (5, 2), and (6, 1), 6 out of the 36 possible pairs, all add to 7. The probability a roll of two dice will add to 7 is 6/36= 1/6. Of course, that means the probability of getting anything other than a 7 rolling a pair of dice is 1 1/6= 5/6. The probability of getting a 7 on the first roll but not on the second is (1/6)(5/6)= 5/36. The probability of getting any number other than a 7 on the first roll but a 7 on the second is (5/6)(1/6)= 5/36. So the probability of getting exactly one 7 in two rolls is (5/36)+ (5/36)= 10/36= 5/18.
All the other problems can be done similarlly. 


#4
May712, 02:13 AM

P: 963

Probability My poor English
Thank you
May I say that what is meant by "2 tosses of a pair of dice" is that it is the random experiment we do and all the outcomes as sample space. My understanding(easy for me to understand graphic presentation) maybe shown below 16not7 (4 dices) 25not7 34not7 43not7 52not7 61not 7 not 7not 7 not 7not 7 ...... OR not716 not725 not 734 ...... 


#5
May2712, 11:58 PM

P: 1




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