Using the tree diagram, you just constructed and make a table showing the probability distribution of getting zero, one, or both questions right by guessing. (i attached the tree diagram)

- hockeychick23

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- hockeychick23

##### 1 Attachment

- hockeychick23

@welshfella @kropot72

- hockeychick23

I got:
Probability of getting zero questions right by guessing: .5626(.75)= .42195
Probability of getting one question right by guessing: (0.75)(.1875)= .140625
(0.25)(.0625)= 0.015625
.140625+0.015625= .15625
but I'm not sure if i did it correctly, can someone check my answer please?

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## More answers

- UnkleRhaukus

don't multiply

- UnkleRhaukus

the number on the right most nodes are the total probabilities already

- hockeychick23

oh ok so the probability of getting zero right is .5625, getting one right is .25+.1875=.4375 and getting both right would be .1875?

- UnkleRhaukus

|dw:1433151671567:dw|

- UnkleRhaukus

yes the probability of getting zero right is .5625,

- UnkleRhaukus

the probability of getting 1 right is the sum of the two probability of the nodes in the tree that are exactly 1 right ansewer

- hockeychick23

yea i got .25+.1875=.4375

- UnkleRhaukus

ie P(1) = P(wr) + P(rw)

- UnkleRhaukus

0.25 is the probability that the first question is right, but we want to add the probabilities that exactly one question is right

- hockeychick23

oh sorry so its .1875+.0625= .25

- UnkleRhaukus

nope

- UnkleRhaukus

|dw:1433152150638:dw|add these

- hockeychick23

.375

- UnkleRhaukus

yes

- hockeychick23

and then both right would be .1875

- UnkleRhaukus

**error in diagram
|dw:1433152335528:dw|

- UnkleRhaukus

there is only one leaf on the tree that has both right answers
P(rr) =

- hockeychick23

yea that leaf says .0625

- UnkleRhaukus

|dw:1433152413453:dw|

- UnkleRhaukus

yes,

- hockeychick23

i think i drew my diagram wrong when i constructed it

- UnkleRhaukus

why do you say that?
it seems right to me
its multiple choice (four options) two questions

- hockeychick23

oh i just flip flopped the wrong and right on the second leaf

- UnkleRhaukus

ah yeah

- UnkleRhaukus

if we add up all the probabilities
P(0) = 0.5625
P(1) = 0.1875+0.1875
= 0.3750
P(2) = 0.0625
P(0)+P(1)+P(2) = 1

- hockeychick23

oh awesome! so if i made it into a table like it was asking could i just draw it like this:

##### 1 Attachment

- UnkleRhaukus

wcheck that last entry in the table again

- hockeychick23

oh its not .1875? I thought that was what it was

- hockeychick23

oh its .375

- UnkleRhaukus

for both right: 1/4 * 1/4 =

- UnkleRhaukus

nope 0.375 is for exactly 1 right

- hockeychick23

##### 1 Attachment

- hockeychick23

sorry i typed it incorrectly, this is the table

- UnkleRhaukus

now to be sure check the sum all the probabilities
.5625 + .375 + .0625 =

- hockeychick23

.5625+.375+0.0625=1

- UnkleRhaukus

Yay!

- hockeychick23

:) thanks so much!!

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