Alfonso and Colin each bought one raffle ticket at the state fair. If 50 tickets were randomly sold,

kazue72949lard

kazue72949lard

Answered question

2022-05-09

Alfonso and Colin each bought one raffle ticket at the state fair. If 50 tickets were randomly sold, what is the probability that Alfonso got ticket 14 and Colin got ticket 23?

The answer should be 1 2450 which presumably comes from 1 50 × 1 49 . But it seems that the order does not count. I did not assume that Alfonso got ticket 14 first then Colin got ticket 23 second.

Update: What is wrong with this reasoning. When I said that I did not assume order, I meant that it's possible

1. Alfonso got ticket 14 first, then Colin got ticket 23,
2. Colin got ticket 23 first, then Alfonso got ticket 14.

Both of these possibilities are possible before the tickets are given out, so we can make an 'or' statement. Label the event Alfonso got ticket 14 by A 14 and Colin got ticket 23 by A 23 . Then by the addition rule
Pr (  ( A 14  first and  C 23  second) or ( C 23  first and  A 14  second ) ) = Pr ( A 14 ) × Pr ( C 23 A 14 ) + Pr ( C 23 ) × Pr ( A 14 C 23 ) = 1 50 × 1 49 × 2.
I realize that once the tickets are sold, then only one of { A 14 C 23   ,   C 23 A 14 } must occur, but before the tickets are sold both possibilities are plausible. Why would the probability change before and after the tickets are sold.

Answer & Explanation

Lara Alvarez

Lara Alvarez

Beginner2022-05-10Added 14 answers

It's not about the order in which they get the tickets, it's about who gets which ticket. When you write 1 50 C 2 , you are saying that there is only one acceptable pair of tickets out of 50 C 2 possible pairs. But after you choose the correct pair, you still have to say who gets ticket 14 and who 23, and there is only one way to do that correctly out of two possibilities.
vilitatelp014

vilitatelp014

Beginner2022-05-11Added 6 answers

"I did not assume that Alfonso got ticket 14 then Colin got ticket 23" - order in this sense has nothing to do with time. It is a question of whether or not

Alfonso got ticket 14 and Colin got ticket 23

is different from

Alfonso got ticket 23 and Colin got ticket 14.

And clearly it is different, and only the first is asked for in your problem. There are 50 × 49 ways in which tickets could be allocated to A and C, with order (in the sense I have just explained) being important; and only one successful case; so the probability is
1 50 × 49   .

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