Edexcel s1 probability question

Hi,

Given P(A)= 0.2 and P(A U B)= 0.6

Find P(A'^B )

^ is the intersection symbol !

Cheers

(edited 8 years ago)

so i will work through this as i type:

A U B is 0.6, A is 0.2 , so then, the Probability that B n A', will be 0.4.
now i am assuming the two events are independent, so B x A will equal B n A

so P A x P B will be P A n B
P A is 0.2
P B is 0.4+(0.2-x) (x being A n B)

0.2 x (0.4 + 0.2 -x) = x

0.12 - 0.2x = x
0.12 = 1.2x
x= 0.1

so p A n b is 0.1
p a' n b is 0.1
p a n b' is 0.4

hope this is correct!! might be wrong since i assumed independence. do you have the mark scheme

(edited 8 years ago)

Reply 2

student97

Original post by TSR-addict

Hi,

Given P(A)= 0.2 and P(A U B)= 0.6

Find P(A'^B )

^ is the intersection symbol !

Cheers

forgot to quote you, don't know if that matters :h:

Reply 3

M.C. Math

Original post by TSR-addict

Hi,

Given P(A)= 0.2 and P(A U B)= 0.6

Find P(A'^B )

^ is the intersection symbol !

Cheers

Hi. An alternative approach that may work for some is to use Venn Diagrams on these type of questions. See the attachment below.

As P(A)=0.2 and P(A U B) = 0.6, then the bit that is in B only is 0.6 - 0.2, i.e. 0.4.

P(A' ^ B) is that part of B that intersects with everything not in A.

(edited 8 years ago)

tempStudentRoomAnswer.png24.2KB

cheers all

And one more thing, when they ask 'what is the probability of event p and event q occuring'' does that mean P intersection Q or P Union Q? Whats the difference between the 2 cheers

Reply 6

M.C. Math

Original post by TSR-addict

And one more thing, when they ask 'what is the probability of event p and event q occuring'' does that mean P intersection Q or P Union Q? Whats the difference between the 2 cheers