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# Suppose we have a bag with 10 slips of paper in it. Eight of these have a 2 on them and the other two have a 4 on them.

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a.) What is the expected value of the number shown when we draw a single slip of paper?

b.) What is the expected value of the number shown if we add one additional 4 to the bag?

c.) What is the expected value of the number shown if we add two additional 4's (instead of just one) to the bag?

d.) How many 4's do we have to add to make the expected value equal to 3?

Mar 29, 2018

### 2+0 Answers

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a.) What is the expected value of the number shown when we draw a single slip of paper?

E = (8*2 + 2*4)/(8 + 2) → 2.4

b.) What is the expected value of the number shown if we add one additional 4 to the bag?

E = (8*2 + 3*4)/(8 + 3) → 2.545...

Now try c) and d) yourself.

Mar 29, 2018
#2
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Thanks, Alan.....here's  the last two

c)

[ 8*2  + 4*4]  / [ 8 + 4 ]  = [ 16 + 16] / [ 12 ]   =  32/12  =  8/3

d) We need to solve this for N

[ 8*2  + N*4] / [ 8  + N ]  =  3

[ 16 + 4N]  =  3 [ 8 + N ]

16 + 4N  =  24 + 3N

N  =  8  ⇒  number of 4's  we need to have to have an expected value of 3

So....we need to add N - 2  =   8 - 2   =   6   Mar 29, 2018