Class 9 Maths Chapter 13 Question Answers - Statistics

Q1. Give three examples of data which you can get from your day-to-day life.
Sol:
Here are the three examples which are related to our day-to-day life:

• The number of boys in a sports team.
• Electricity bills for last one year.
• The number of students appearing for board exams at your school.

Q2: The number of family members in 10 flats of society are
2, 4, 3, 3, 1,0,2,4,1,5.
Find the mean number of family members per flat.
Sol:
Number of family members in 10 flats -2, 4, 3, 3, 1, 0, 2, 4, 1, 5.
So, we get,
Mean = sum of observation/ total no of observations
Mean = (2 + 4+ 3 + 3 + 1 + 0 + 2 + 4 + 1 + 5) / 10
Mean = 25/10 = 2.5

Q3: The daily minimum questions solved by a student during a week were as under:

Find the mean.
Sol:
Number of questions solved in a week: 35, 30, 27, 32, 23, 28.
So, we get,
Mean = sum of observation/ total no of observations = (35+30+27+32+23+28) / 6 = 175/6 = 29.167

Q4: The mean weight of a class of 34 students is 46.5 kg. If the weight of the new boy is included, the mean is rises by 500 g. Find the weight of the new boy.
Sol:
The mean weight of 34 students = 46.5
Sum of the weight of 34 students = (46.5 * 34) = 1581
Change or increase in the mean weight when the weight of a new boy is added = 0.5
So, the new mean = (46.5 +0.5) = 47
So, let the weight of the new boy be y.
So, (sum of weight of 34 students + weight of new boy) / 35 = 47
(1581+ y)/ 35 = 47
1581 + y = 1645
y = 1645 – 1581 = 64

Q5: The height of 20 students of class V are noted as follows

4, 4.5, 5, 5.5, 4, 4, 4.5, 5, 5.5, 4, 3.5, 3.5, 4.2, 4.6, 4.2, 4.7, 5.5, 5.3, 5, 5.5.

• Make a frequency distribution table for the above data.
• Which is the most common height and which is the rarest height among these students?

Sol:

1. The required frequency distribution table is:

2. The most common heights are 4 and 5.5.
The rarest heights are 4.6 and 4.7.

Q6: The following is the list of number of coupons issued in a school canteen during a week:
105, 216, 322, 167, 273, 405 and 346.
Find the average no. of coupons issued per day.
Sol:
Number of coupons issued in a week: 105, 216, 322, 167, 273, 405 and 346.
So, we get,
Mean = sum of observation/ total no of observations
Mean = (106+ 215+ 323+166+273+405+346)/ 7 = 1834/7
Mean = 262

Q7: If the mean of six observations y, y + 1, y + 4, y + 6, y + 8, y + 5 is 13, find the value of y.
Sol:
Mean = sum of observation/ total no of observations
13 = (y + y + 1+ y + 4+ y + 6+ y + 8+ y + 5) / 6
13 = (6y + 24)/6
(13 * 6) = 6y +24
(13 * 6) – 24 = 6y
(13 * 6) – 6 * 4 = 6y
6(13 – 4) = 6y
y = 9

Q8: The Number of books issued to 13 students in a class are:
25, 19, 24, 23, 29, 31, 19, 20, 22, 26, 17, 35, 21.
Find the median no. of books for the above data.
Sol:
Let’s arrange the data given in ascending order – 17, 19, 19, 20, 21, 22, 23, 24, 25, 26, 29,31,35.
n= 13, so it’s an odd number
Median = (n+1) / 2 observations
= (13+1)/ 2 = (14/2)th observation = 7th observation = 23

Q9: The weight (in kg) of 7 students of a class are 44, 52, 55, 60, 50, 49, 45.
Find the median weight.
Sol:
Let’s arrange the data given in ascending order – 44, 45, 49, 50, 52, 55, 60.
n= 7, so it’s an odd number
Median = (n+1) / 2 observations
= (7+1)/ 2 = (8/2)th observation = 4th observation = 50 kg