Class 9 Maths Chapter 13 Question Answers - Statistics

Question 1. In Summer vacations, Puneet motivated 500 people for blood donation and for this social work he received a cash award of ₹ 10,000. His father advised him to make a budget plan for spending this amount.
 He made the following plan :

(a) Make a pie-chart for the above data.
(b) Which mathematical concept has been covered in the above problem?
(c) Which values are depicted by Puneet in his budget plan?
 Sol. (a) To make a pie-chart, we have to determine central angles corresponding to various heads :

S.No.	Head	Amount (₹)	Central angle
	Total	10,000	360°

The required pie-chart is as given below :

(b) Statistics

(c)(i) gainful use of prize money
(ii) charity
(iii) caring for others

Question 2. 90 schools participated in a plantation programme. Each school planted 100 plants. After one month the number of plants that survived were recorded as :

(a) Present the data in a frequency table using classes 20-29, 30-39, ..... 90-99.
(b) From the table find the number of schools where 50% or more plants survived?
(c) Which mathematical concept is used in the above problem?
(d) By taking part in the plantation programme which value is depicted by the participating schools?
 Sol. (a) The required frequency table is given as:

(b) Total number of plants planted by each school = 100
∴ 50% of 100 = 50
⇒ Number of schools where 50% or more plants survived = 07 + 16 + 09 + 22 + 12 = 66
(c) Statistics
(d) Betterment of environment.

Question 3. 40 students of class IX contributed different amounts to Prime Minister’s Relief Fund. Vinod and Preeti were assigned to determine the mean amount of the class. Vinod comes out with his answer as ₹160 but Preeti found that the value of ₹165 was wrongly copied as ₹125 by Vinod and she gave the correct answer.

(a) Find the correct mean.
(b) Which concept of mathematics is used in the above problem?
(c) Which values are depicted by Preeti and other students of class IX?
 Sol. (a) Total number of students = 40
⇒ Number of observations = 40
∵ Mean calculated by Vinod = 160
∵ Total of 40 observations = 40 × 160 = 6400
But the observation 165 is recorded as 125
∴ Actual total of the 40 observations = (6400 – 125) + 165 = 6440
⇒ Correct mean calculated by Preeti = (6440/40)= 161
Thus, the correct mean is 161.

(b) Statistics

(c)(i) Accuracy
(ii) Patriotism

Question 4. Mrs. Prabha is a mathematics teacher in a school. She motivated 60 students from 2 sections of class IX to appear in proficiency-test in mathematics. The marks obtained by the students are as :

(b) From the above frequency-table, we find that :
Number of students securing more than 49 marks = 12 + 10 + 6 + 3 + 1 =32
(c) Statistics
(d) Group inspiration.

Question 5. 30 students from senior classes of a school plan to donate blood in a blood donation camp.
 Their blood groups are recorded as follows :

(a) Represent the given data in the form of a frequency distribution table.
(b) Which is the most common blood group?
(c) Which mathematical concept is used in the above problem?
(d) By donating blood, which value is depicted by the students of senior classes?
 Sol. (a)

(b) The most common blood group is ‘O’.

(c) Statistics

(d) Sacrificial act.