### Probability of a single event

```Probability of a single event
Friday, July 17, 2015
Example
John has these 5 coins.
John is going to take one of these coins at random.
Each coin is equally likely to be the one he takes.
a) What is the probability that it will be a 10p coin he selects?
b) What is the probability that it will be a £1 coin he selects?
c) What is the probability that it will be a 1p coin he selects?
Example
A spinner has seven equal sections.
1
4
3
8
4
7
9
(a) What is the probability of scoring 4 on the spinner?
(b) What is the probability of scoring an even number on the spinner?
(c) What is the probability of scoring a prime number on the spinner?
Example
A single card is drawn from a pack of 52 playing cards. Find the probability of the
card being:
(a)
a Queen
(b)
a club
(c)
the Jack of hearts
(d)
an even number.
(e)
a picture card
Example
The set of lottery balls are placed into the drum for the Saturday draw.
What is the probability that the first ball out of the drum is
a)
the number 17
b) an even number
c)
a prime number
d) a factor of 20
e) a multiple of 5?
Example
A letter is selected at random from the word
the probability that it is:
(i)
ah
(ii) a consonant
(iii) a m?
Mathematics. What is
Example
A bag contains 9 white balls, 8 green balls and 3 blue balls. One ball is selected
at random. What is the probability that the ball is
(a)
white
(b)
green
(c)
red
(d)
not blue?
Example
A bag contains some counters of various colours. A counter is taken at random
from the bag and the table below shows the probability of the counter being
red, green, yellow, or blue.
Colour
Red
Green
Yellow
Blue
a)
Probability
0.3
0.4
0.1
Work out the probability of the counter being blue.
b) Work out the probability of the counter being red or green.
Example
The table below shows the eating arrangements for some 150 students.
Complete the table
School
Packed
Eats out
Total
Lunch
Lunch
Male
20
74
Female
Total
13
58
45
150
One student is selected at random.
a) What is the probability that the student selected
(i) Has a school lunch?
(ii) Is male and eats out at lunchtime?
(iii) Is female?
b) Given that it was a male selected, what is the probability that they brought a
packed lunch to school?
Example
The Local supermarket sends a questionnaire to a random sample of 40 workers during a
week in December.
One of the questions is:
How many hours did you work last week?
The results are given in the table below.
Hours worked in week t
25 ≤  ≤ 30
30 ≤  ≤ 35
35 ≤  ≤ 40
40 ≤  ≤ 45
45 ≤  ≤ 50
50 ≤  ≤ 55
Number of staff
3
8
12
7
6
4
Based on the sample below if a member of staff in the supermarket is selected at random
what is the probability that the member
a) Worked between 30 and 35 hours last week?
b) Worked over 40 hours last week?
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