Apps. and Interpretation for IBDP Maths Ebook 1 | Page 300

Your Practice Set – Applications and Interpretation for IBDP Mathematics
(d)
The probability that Ruby does not go to school
by taxi
�(1 � 0.292) n
(M1) for valid approach
� 0.708 n
n
1�0.708 � 0.9
(M1)(A1) for correct inequality
n
0.1�0.708 � 0
By considering the graph of
y �0.1� 0.708 n ,
n � 6.6681451
(A1) for correct value
�n
� 7
A1 N5
[5]
Exercise 85
1. There are six working days for Joyce per week. She can either choose going back to
office to work or stay at home to work. When it snows, the probability that she goes to
office is 0.12. When it does not snow, the probability that she goes to office is 0.76. The
probability that it snows on any given day is 0.56.
(a)
(b)
(c)
(d)
On a randomly selected working day, find the probability that Joyce goes to
office.
[3]
Given that Joyce goes to office to work on a particular day, find the probability
that it was not snowing.
[3]
In a randomly chosen working week, find the probability that Joyce stay at home
to work on exactly four days.
[3]
After n working days, the probability that Joyce stay at home to work at least
once is greater than 0.84. Find the least value of n .
[5]
2. Anson goes to school four days a week. He travels to school either by car or by bicycle.
On any particular day the probability that he travels by car is 0.4.
The probability of being late for school is 0.2 if he travels by car.
The probability of being late for school is 0.3 if he travels by bicycle.
(a)
(b)
On a randomly selected school day, find the probability that Anson is late.
Given that Anson is late on a particular school day, find the probability that he
travels by bicycle.
[3]
[3]
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