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13 questions · self-marked practice — reveal the answer and mark yourself.

Question 12 Marks
Find the mean of all factors of 10
Answer
The factors of 10 are 1, 2, 5 and 10.
Let $\bar{\text{x}}$ denote their arithmetic mean. Then,
$\bar{\text{x}}$ = (1 + 2 + 5 + 10) ÷ 4
= 18 ÷ 4
= 4.5
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Question 22 Marks
Find the mean of 994, 996, 998, 1002 and 1000.
Answer
Mean = Sum of the observations ÷ Total number of observations
Mean = (994 + 996 + 998 + 1002 + 1000) ÷ 5
= 4990 ÷ 5
= 998
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Question 32 Marks
Ashish studies for 4 hours, 5 hours and 3 hours on three consecutive days. How many hours does he study daily on an average?
Answer
Average number of study hours = (4 + 5 + 3) ÷ 3
= 12 ÷ 3
= 4 hours
Thus, Ashish studies for 4 hours on an average.
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Question 42 Marks
Find the mode of the data: 2, 6, 5, 3, 0, 3, 4, 3, 2, 4, 5, 2, 4
Answer
Arranging the data in ascending order such that same values are put together, we get:
0, 2, 2, 2, 3, 3, 3, 4, 4, 4, 5, 5, 6
Here, 2, 3 and 4 occur three times each. Therefore, 2, 3 and 4 are the three modes.
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Question 52 Marks
A cricketer scores the following runs in 8 innings: 58, 76, 40, 35, 48, 45, 0, 100. Find the mean score.
Answer
We have:
The mean score = (58 + 76 + 40 + 35 + 48 + 45 + 0 + 100) ÷ 8
= 402 ÷ 8
= 50.25 runs.
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Question 62 Marks
Find the mean of first five multiples of 3
Answer
The first five multiples of 3 are 3, 6, 9, 12 and 15.
Let $\bar{\text{x}}$ denote their arithmetic mean. Then,
$\bar{\text{x}}$ = (3 + 6 + 9 + 12 + 15) ÷ 5
= 45 ÷ 5
= 9
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Question 72 Marks
The marks (out of 100) obtained by a group of students in science test are 85, 76, 90, 84, 39, 48, 56, 95, 81 and 75. Find the
Mean marks obtained by the group.
Answer
In order to find the highest and lowest marks, let us arrange the marks in ascending order as follows:
39, 48, 56, 75, 76, 81, 84, 85, 90, 95
We have:
Mean marks = Sum of the marks ÷ Total number of students
Mean marks = (39 + 48 + 56 + 75 + 76 + 81 + 84 + 85 + 90 + 95) ÷ 10
= 729 ÷ 10
= 72.9.
Hence, the mean mark of the students is 72.9.
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Question 82 Marks
Find the mean of first five natural numbers.
Answer
The first five natural numbers are 1, 2, 3, 4 and 5.
Let $\bar{\text{x}}$ denote their arithmetic mean. Then,
$\bar{\text{x}}$ = (1 + 2 + 3 + 4 + 5) ÷ 5
= 15 ÷ 5
= 3
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Question 92 Marks
Find the median and mode of the data: $35,32,35,42,38,32,34$
Answer
Arranging the data in ascending order such that same numbers are put together, we get:
$32,32,34,35,35,38,42$
Here, $n =7$
Median $=$ value of $\frac{ n +1}{2}$ th observation $=$ value of the $4^{\text {th }}$ observation $=35$
Here, 32 and 35 , both occur twice. Therefore, 32 and 35 are the two modes.
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Question 102 Marks
If the heights of 5 persons are 140cm, 150cm, 152cm, 158cm and 161cm respectively, find the mean height.
Answer
The mean height = Sum of the heights ÷ Total number of persons
= (140 + 150 + 152 + 158 + 161) ÷ 5
= 761 ÷ 5
= 152.2cm.
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Question 112 Marks
Find the mean of x, x + 2, x + 4, x + 6, x + 8.
Answer
Mean = Sum of observations ÷ Number of observations
⇒ Mean = (x + x + 2 + x + 4 + x + 6 + x + 8) ÷ 5
⇒ Mean = (5x + 20) ÷ 5
⇒ Mean = 5(x + 4)5
⇒ Mean = x + 4
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Question 122 Marks
The enrolment of a school during six consecutive years was as follows:
1555, 1670, 1750, 2019, 2540, 2820
Find the mean enrollment of the school for this period.
Answer
The mean enrolment = Sum of the enrolments in each year ÷ Total number of years
The mean enrolment = (1555 + 1670 + 1750 + 2019 + 2540 + 2820) ÷ 6
= 12354 ÷ 6
= 2059.
Thus, the mean enrolment of the school for the given period is 2059.
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Question 132 Marks
Find the mean of first 10 even natural numbers.
Answer
The first 10 even natural numbers are 2, 4, 6, 8, 10, 12, 14, 16, 18 and 20.
Let $\bar{\text{x}}$ denote their arithmetic mean. Then,
$\bar{\text{x}}$ = (2 + 4 + 6 + 8 + 10 + 12 + 14 + 16 + 18 + 20) ÷ 10
= 110 ÷ 10
= 10
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