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Question 12 Marks
The percentages of marks obtained by a student in six unit tests are given below:
Unit test
I
II
III
IV
V
VI
Percentage of marks obtained
53
72
28
46
67
59
A unit test is selected at random. What is the probability that the student gets more than 60% marks in the test?
Answer
Number of tests in which he gets more than 60% marks = 2
Total numbers of tests = 6
$\therefore$ Required probability $=\frac{\text{Number of tests in which he gets more than 60% marks}}{\text{Total number of trials}}$
$=\frac{2}{6}=\frac{1}{3}$
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Question 22 Marks
The marks obtained by 90 students of a school in mathematics out of 100 are given as under:
Marks
0 - 20
20 - 30
30 - 40
40 - 50
50 - 60
60 - 70
70 and above
Number of students
7
8
12
25
19
10
9
From these students, a student is chosen at random.
What is the probability that the chosen student:
  1. Gets 20% or less marks?
  2. Gets 60% or more marks?
Answer
Total number of patients = 90
  1. Probability that the chosen student gets 20% or less marks $=\frac{7}{90}$
  2. Probability that the chosen student gets 60% or more marks $=\frac{10+9}{90}=\frac{19}{90}$
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Question 32 Marks
12 Packets of salt, each marked 2kg, actually contained the following weights (in kg) of salt:
1.950, 2.020, 2.060, 1.980, 2.030, 1.970, 2.040, 1.990, 1.985, 2.025, 2.000, 1.980.
Out of these packets, one packet is chosen at random.
What is the probability that the chosen packet contains more than 2kg of salt?
Answer
Total number of salt packets = 12
Number of packets containing more than 2kg of salt = 5
Therefore, 
Probability that the chosen packet contains more than 2kg of salt $=\frac{\text{No. of packets containing more than 2kg of salt}}{\text{Total number of salt packets}}$
$=\frac{5}{12}$
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Question 42 Marks
On a particular day, at a crossing in a city, the various types of 240 vehicles going past during a time interval were observed, as under:
Types of vehicle
Two-wheelers
Three-wheelers
Four-wheelers
Frequency
84
68
88
Out of these vehicles, one is chosen at random. What is the probability that the chosen vehicle is a two-wheeler?
Answer
Total number of vehicles going past the crossing = 240
Number of two-wheelers = 84
Let E be the event that the selected vehicle is a two-wheeler. Then,
required probability = P(E) $=\frac{84}{240}=0.35$
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