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Bunuel
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Hi,

Same question. Why do we not include 1,1 2,2 & 3,3 ?
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nidhihiremath
Hi,

Same question. Why do we not include 1,1 2,2 & 3,3 ?

It is like the Set consists of 9 balls numbered 1-9 and you are picking two balls. Hence you cant pick the same ball twice. I think in a set repetitions are meaningless. Correct me if wrong
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Bunel please help. It is given that {X = a, Y = b} is the same as the event {X = b, Y = a} for any numbers a and b in A,. So a=b is a possibility. It is no where given that a and b are distinct. Then why we avoided pairs like (1,1)?
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we can select only pairs (1,2), (1,3), (1,4), (1,5), (2,3), (2,4) and (3,4) = total 7 and if we say reverse is also true then total no of probable selections = 14

Total ways to select 2 numbers from 10 = 10*9 = 90 ways

hence probability = 14/90 = 7/45 (ans)
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Bunuel why we can’t choose same number such as (1,1) (2,2)(3,3)(4,4)?

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Because, you need to select 2 numbers from the set without keeping back the 1st number from (1 to 10), thats why pair is not possible and thats why total no of ways we can do it 10X9 = 90
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pudu
Bunel please help. It is given that {X = a, Y = b} is the same as the event {X = b, Y = a} for any numbers a and b in A,. So a=b is a possibility. It is no where given that a and b are distinct. Then why we avoided pairs like (1,1)?

please someone help me to understand it...why we are not taking x=y?
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zahuruddin
Because, you need to select 2 numbers from the set without keeping back the 1st number from (1 to 10), thats why pair is not possible and thats why total no of ways we can do it 10X9 = 90

but it is not given repetition is not allowed?then why we assume so?
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