Question

There is a 0.63 probability that Mobil stock will rise, a 0.75 probability Gulf stock will rise and a 0.4 chance that both stocks will rise. Find the probability that neither stock will rise. There is a 0.63 probability that Mobil stock will rise, a 0.75 probability Gulf stock will rise and a 0.4 chance that both stocks will rise. Find the probability that neither stock will rise. @Mathematics

Answer 1

So .37*.25=.0925

But the answer key for a similar problem( only difference is .47 instead of .4), the answer is .2775. The answers shouldnt differ that much right?

Answer 2

why are you multiplying those two numbers?

Answer 3

isnt that how you get the probability for AND?

Answer 4

not in this case

Answer 5

Then Im completely lost.

Answer 6

your events are NOT independent

Answer 7

I think that's the concept that I dont quite understand

Answer 8

would the formula be P(A U B)/P(A)?

Answer 9

no

Answer 10

use \[P(A^c\cap B^c)=1-P(A\cup B)\]

Answer 11

so the 1-P(none) formula

Answer 12

for any event E

\[P(E)=1-P(E^c)\]

or \[P(E^c)=1-P(E)\]

Answer 13

so how exactly does not being independent effect the problem?

Answer 14

events A and B are independent iff

\[P(A\cap B)=P(A)P(B)\]

Answer 15

you cant use this formula since A and B are not independent

Answer 16

So in terms of a venn diagram, independent is two circles that dont intersect. and not independent has two circles that do intersect.

and in this problem the intersection is .4?

So I need to find the sum of each part of the venn diagram, subtract from one (to get the number outside the diagram) which would be the "neither". Correct?

Answer 17

NO

Answer 18

independent events intersect (most of the time)

Answer 19

if A and B are independent and P(A)>0 and P(B)>0 then A and B have to intersect.

Answer 20

use

\[P(A^c\cap B^c)=1-P(A\cup B)=1-[P(A)+P(B)-P(A\cap B)]\]

Answer 21

Is what Im picturing

Basically, I was doing P(Ac∩Bc)=1−P(A∪B)=1−[P(A)+P(B)−P(A∩B)] except that mine adds instead of subtracts the intersection.