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s1 question 2016 juneeeeeee

guys in part e why cant we just do 1/E(X)??????
xxx.PNG57.7KB
also here in part f how come we add the probabiliuties and not multiply them!!!!!!!!
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????????? :frown::frown:
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b0bzzta
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Original post by pondsteps
guys in part e why cant we just do 1/E(X)??????


Hi i literally just did this question lol. So basically, for part e I just redrew the table but for Rebecca, have a go at that and it'll all make sense.


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b0bzzta
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Give me a minute i'll show u how i did it


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b0bzzta
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ImageUploadedByStudent Room1495228701.877726.jpg

The red arrows show u when Sarah's score is bigger then Rebecca's. So u just add those up. Do u understand now?


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Original post by b0bzzta
ImageUploadedByStudent Room1495228701.877726.jpg

The red arrows show u when Sarah's score is bigger then Rebecca's. So u just add those up. Do u understand now?


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ohhh what u did makes sense but why doesnt the other way also work!!
Reply 7
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b0bzzta
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Original post by pondsteps
ohhh what u did makes sense but why doesnt the other way also work!!


Just think about it for the first value. When you are calculating E(X) for sarah, you are going to do -2p. For Rebecca you are supposed to do (-1/2)*p=-p/2. Now instead of doing that, if you did 1/E(X), you would get -1/2p which is wrong. Does that help?


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