Class 8 Math Direct And Inverse Proportion Ex13.2 Solution

Class 8 Math Direct and Inverse Proportion Ex13.2 Solve focuses on solving problems related to inverse proportion. This concept explains how one quantity increases as the other decreases, and vice versa. Through real-life examples and word problems, this exercise helps students understand the relationship and apply it effectively in practical situations.

Class 8 Math Direct and Inverse Proportion Ex13.2 Solve

Question 1.
Which of the following are in inverse proportion?
(i) The number of workers on a job and the time to complete the job.
(ii) The time taken for a journey and the distance travelled at a uniform speed.
(iii) Area of cultivated land and the crop harvested.
(iv) The time taken for a fixed journey and the speed of the vehicle.
(v) The population of a country and the area of land per person.

Solution:

(i) As the number of workers increases, the job will take less time to complete. Hence, they are inversely proportional.

(ii) For more time, more distance to travel. Hence, they are not inversely proportional.

(iii) More area of land cultivated means more crop to harvest. Hence, they are not inversely proportional.

(iv) If speed is increased, it will take less time to complete the fixed journey. Hence, they are inversely proportional.

(v) If the population of a country increases, then the area of land per person will decrease. Hence, they are inversely proportional.

Class 8 Math Ch Direct and Inverse Proportion Ex13.2

Ex 13.2 Class 8 Maths Question 2.
In a Television game show, the prize money of ₹ 1,00,000 is to be divided equally amongst the winners. Complete the following table and find whether the prize money given to an individual winner is directly or inversely proportional to the number of winners?

Number of winners	1	2	4	5	8	10	20
The prize for each winner (in ₹)	1,00,000	50,000	–	–	–	–	–

Solution:
Let the blank spaces be denoted by a, b, c, d, and e.
So, we observe that 1 × 100,000 = 2 × 50,000
⇒ 1,00,000 = 1,00,000
Hence they are inversely proportional.

2 × 50,000 = 4 × a

NCERT Solutions for Class 8 Maths Chapter 13 Direct and Inverse Proportions Ex 13.2 Q2.1

Number of winners	1	2	4	5	8	10	20
The prize for each winner (in ₹)	1,00,000	50,000	25,000	20,000	12,500	10,000	5,000

Ex 13.2 Class 8 Maths Question 3.
Rehman is making a wheel using spokes. He wants to fix equal spokes in such a way that the angles between any pair of consecutive spokes are equal. Help him by completing the following table.
NCERT Solutions for Class 8 Maths Chapter 13 Direct and Inverse Proportions Ex 13.2 Q3

Number of spokes	4	6	8	10	12
The angle between a pair of consecutive spokes	90°	60°	–	–	–

(i) Are the number of spokes and the angle formed between the pairs of consecutive spokes in inverse proportion?
(ii) Calculate the angle between a pair of consecutive spokes on a wheel with 15 spokes.
(iii) How many spokes would be needed if the angle between a pair of consecutive spokes is 40°?

Solution:
From the above table, we observe that
4 × 90° = 6 × 60°
360° = 360°
Thus, the two quantities are inversely proportional.

Let the blank spaces be denoted by a, b, and c.
4 × 90° = 8 × a

NCERT Solutions for Class 8 Maths Chapter 13 Direct and Inverse Proportions Ex 13.2 Q3.1

Hence, the required table is

Number of spokes	4	6	8	10	12
The angle between a pair of consecutive spokes	90°	60°	45°	36°	30°

(i) Yes, they are in inverse proportion
(ii) If the number of spokes is 15, then
4 × 90° = 15 × x
x = 4×9015 = 24°
(iii) If the angle between two consecutive spokes is 40°, then
4 × 90° = y × 40°
y = 4×9040 = 9 spokes.
Thus the required number of spokes = 9.

Class 8 Math Ch Direct and Inverse Proportion Ex13.2

Ex 13.2 Class 8 Maths Question 4.
If a box of sweets is divided among 24 children, they will get 5 sweets each. How many would each get, if the number of the children is decreased by 4?
Solution:

Number of children	Number of Sweets
24	5
(24 – 4) or 20	a

We observe that increasing the number of children will result in each receiving fewer sweets. So, they are in inverse proportion.
x₁y₁ = x₂y₂
where x₁ = 24, y₁ = 5, x₂ = 20
and y₂ = a (let)
24 × 5 = 20 × a
a = 6
Hence, the required number of sweets = 6.

Ex 13.2 Class 8 Maths Question 5.
A farmer has enough food to feed 20 animals for 6 days. How long would the food last if there were 10 more animals?

Solution:
If the number of animals increases, then it will take fewer days for the food to last.
Thus, the two quantities are in inverse proportions.

Number of animals	Number of days
20	6
(20 + 10) or 30	P

Let the required number of days be p.
x₁y₁ = x₂y₂
where x₁ = 20, y₁ = 6, x₂ = 3
and y₂ = p (let)
20 × 6 = 30 × p
p = 4
Hence the required number of days = 4.

Class 8 Math Ch Direct and Inverse Proportion Ex13.2

Ex 13.2 Class 8 Maths Question 9.
A car takes 2 hours to reach a destination while traveling at a speed of 60 km/h. How long will it take when the car travels at the speed of 80 km/h?

Solution:
On increasing the speed, it will take less time to travel the same distance.
Thus, the two quantities are in inverse proportions.

Number of persons	Number of days
3	4
4	k

Let the required number of days be k.
x₁y₁ = x₂y₂
3 × 4 = 4 × k
k = 3 days.
Hence, the required number of days = 3.

Class 8 Math Ch Direct and Inverse Proportion Ex13.2

Ex 13.2 Class 8 Maths Question 7.
A batch of bottles was packed in 25 boxes with 12 bottles in each box. If the same batch is packed using 20 bottles in each box, how many boxes would be filled?
NCERT Solutions for Class 8 Maths Chapter 13 Direct and Inverse Proportions Ex 13.2 Q7
Solution:
If the number of bottles is increased then the required number of boxes will be decreased. Thus the two quantities are in inverse proportion.

Number of boxes	Number of bottles per box
25	12
x	20

Let the required number of boxes be x.
x₁y₁ = x₂y₂
25 × 12 = x × 20
x = 15
Hence, the required number of boxes = 15.

Class 8 Math Ch Direct and Inverse Proportion Ex13.2

Ex 13.2 Class 8 Maths Question 8.
A factory requires 42 machines to produce a given number of articles in 63 days. How many machines would be required to produce the same number of articles in 54 days?
Solution:
If the number of machines is increased then less number of days would be required to produced the same number of articles.
Thus, the two quantities are in inverse proportion.

Number of machines	Number of days
42	63
x	54

Let the required number of machines be x.
x₁y₁ = x₂y₂
42 × 63 = x × 54
x = 49
Hence, the required number of machines is 49.

Ex 13.2 Class 8 Maths Question 9.
A car takes 2 hours to reach a destination by traveling at a speed of 60 km/h. How long will it take when the car travels at the speed of 80 km/h?
Solution:
On increasing the speed, it will take less time to travel a distance.
Thus the two quantities are in inverse proportions.

Speed in km/h	Time in hour
60	2
80	x

Let the required times be x hours.
x₁y₁ = x₂y₂
60 × 2 = 80 × x
x = 32 hours = 112 hrs.
Hence, the required time = 112 hours.

Ex 13.2 Class 8 Maths Question 10.
Two persons could fit new windows in a house in 3 days.
(i) One of the people fell ill before the work started. How long would the job take now?
(ii) How many persons would be needed to fit the windows in one day?
Solution:
On increasing the number of persons, less time will be required to complete a job.
Thus, the quantities are in inverse proportion.

Number of persons	Number of days
2	3
(i) 1(2 – 1)	x
(ii) y	1

(i) Let the required number of days be x.
x₁y₁ = x₂y₂
2 × 3 = 1 × x
x = 6
Hence, the required number of days = 6
(ii) Let the required number of persons be y.
x₁y₁ = x₂y₂
2 × 3 = y × 1
y = 6
Hence, the required number of persons = 6.

Class 8 Math Ch Direct and Inverse Proportion Ex13.2

Ex 13.2 Class 8 Maths Question 11.
A school has 8 periods a day each of 45 minutes duration. How long would each period be, if the school has 9 periods a day, assuming the number of school hours to be the same?
Solution:
On increasing the duration of periods, the number of periods will be reduced.
Thus, the two quantities are in inverse proportion.