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What is the probability that he is having pizza?

navi

New member
Mar 25, 2018
12
Hi! So I am confused with this problem:

Homer watches Monday Night Football with a probability .6, he has pizza on Monday night with a probability .45, and he does both with probability .25. When you call him on Monday night, you learn that he is watching Monday Night Football. What is the probability that he is having pizza?

The answer is 5/12, I don't understand why :(

First of all, I do not understand how the probability of doing both is .25. Should it not be .6*.45? So, the formula should be for Probability of having pizza given that he is watching MNF, which would be: (.6*.45)/(.6*.45)+(.45*.4)... but I am obviously doing something wrong... :(
 

tkhunny

Well-known member
MHB Math Helper
Jan 27, 2012
267
Hi! So I am confused with this problem:

Homer watches Monday Night Football with a probability .6, he has pizza on Monday night with a probability .45, and he does both with probability .25. When you call him on Monday night, you learn that he is watching Monday Night Football. What is the probability that he is having pizza?

The answer is 5/12, I don't understand why :(

First of all, I do not understand how the probability of doing both is .25. Should it not be .6*.45? So, the formula should be for Probability of having pizza given that he is watching MNF, which would be: (.6*.45)/(.6*.45)+(.45*.4)... but I am obviously doing something wrong... :(
.25 is not calculated from .6 and .45. It is given.

Draw two separate circles.

Label one "p( Football ) = 0.60"
Label the other "p( Pizza ) = 0.45"
Now, slide them together until they overlap.
--- Label the overlap "p(Both) = 0.25".
--- Put 0.60 - 0.25 = 0.35 in the football lune
--- Put 0.45 - 0.25 = 0.20 in the pizza lune

If you have the picture right, you should be able to answer the questions.

Are there more weird icons that can be developed from simple words? ( P i z z a ) gives (Pizza).