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Here is the question link:

https://vle.mathswatch.co.uk/images/questions/question2769.png

Both A and B please

 May 14, 2020
 #1
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There are 7 tiles, 2 of which are 1s.

 

so thus we have a 2/7 probability of drawing one for the first drawings, (2-1)/(7-1) = 1/6 for the second.


Multiplying the 2 gives 2/42 = 1/21.

 

Let's use casework for 2.

 

If he picks a 1, 2/7 probability, he then can choose 3 or 5, so 5/(7-1) = 5/6 probability. 10/42 = 5/21 probaility if he gets one first.

 

If he picks a 3, 3/7 probibiliity, he then can choose 5, so 2/(7-1) = 2/6= 1/3 probaility. The 3's cancel out so we have 1/7 probability.

 

If he picks 5 then we don't consider that, no larger.

 

We add the two probabilities and get 5/21 + 3/21 = 8/21.

 

If you don't understand anything feel free to ask.

 May 14, 2020
 #2
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No thanks I understand that, thank you for the help!

Guest May 14, 2020
 #3
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No problem!

 

laugh

hugomimihu  May 14, 2020

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