The Student Room Group

This discussion is now closed.

Check out other Related discussions

Probability question

In testing the water supply in various cities for two kinds of impurities commonly found in water, it was found that 20% of the water supplies had neither sort of impurity, 40% had an impurity of type A, and 50% had an impurity of type B. If a city is chosen at randomfind the probability that its water supply has

(i) both types of impurities,
(ii) exactly one type of impurity,
(iii) only type B impurity
------------------------------------------------------------------------------------

(i) P(N)+P(A u B)=1
P(A u B)=1-P(N)=1-0.2=0.8

P(A u B)=P(A)+P(B)-P(A n B)
P(A n B)=P(A)+P(B)-P(A u B) = 0.4 + 0.5 - 0.8 = 0.1

(ii) P( (A n B') u (A' n B) )
= [P(A)-P(A n B)] + [P(B)-P(A n B)]
=(0.4-0.1)+(0.5-0.1) = 0.7

(iii) P(B n A') = P(B) - P(A n B) = 0.5 - 0.1 = 0.4

is this correct? thanks
That all looks good to me.

Related discussions

Latest

Trending

Trending

Articles for you