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October 25th, 2017, 09:14 PM   #1
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From: Camboja

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I need help to calculate a simple problem in probability

Hi folks, i'm not from math field, but i have a question,

1- If in 10 times of event A will occur 2 times event B inside A

2- i know that the chance of event B to occur in sequence is 9, right?

x x | | | | | | | | 1

| x x | | | | | | | 2

| | x x | | | | | | 3

| | | x x | | | | | 4

| | | | x x | | | | 5

| | | | | x x | | | 6

| | | | | | x x | | 7

| | | | | | | x x | 8

| | | | | | | | x x 9


3- Then i question, how can i calculate how many times can event B occur NOT in sequence? and how to calculate it?

for example

| x | x | | | | | |


thanks a lot for any help
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October 25th, 2017, 10:52 PM   #2
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There are $\dbinom{10}{2}=45$ ways that 2 x's can occur out of the 10 events.

You showed there are 9 ways that the two x's can occur sequentially.

Thus there are 45-9=36 ways the two x's can occur non-sequentially.

Last edited by romsek; October 25th, 2017 at 10:55 PM.
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October 25th, 2017, 10:59 PM   #3
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thanks for answering, i was thinking it was way more thank 100 possibilities, have a nice day
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