18. Leah is visiting Cardiff. The probability that she will go on a tour bus is 0·3. The probability of Leah seeing a show at the Millennium Centre is independent of her going on a tour bus.
The probability that she goes on a tour bus and sees a show at the Millennium Centre is 0·24.
(a) Complete the following tree diagram. [4]
(b) Calculate the probability that Leah does not go on a tour bus and does not see a show at the Millennium Centre. [2]
Mark scheme (a)
Scheme
Marks
Comments
0·7 shown for ‘Does not go on tour bus’.
B1
Use of 0·3 × …… = 0·24
M1
P(sees show) = 0·8
A1
Allow M1A1 if 0·8 seen on one of the ‘sees show’ branches.
Second set of branches 0·8, 0·2, 0·8, 0·2
A1
FT ‘their 0·8’ only if M1 awarded. (0·24, 0·76, 0·24, 0·76 is M0A0A0)
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