Chapter 13 Direct and Inverse Proportions

Exercise 13.1

Ex 13.1 Class 8 Maths

Question 1.
Following are the car parking charges near a railway station up to.
4 hours – ₹ 60
8 hours – ₹ 100
12 hours – ₹ 140
24 hours – ₹ 180
Check if the parking charges are in direct proportions to the parking time.

Solution:
We have the ratio of time period and the parking charge.

Hence the given quantities are not directly proportional.

Ex 13.1 Class 8 Maths 

Question 2.
A mixture of paint is prepared by mixing 1 part of red pigments with 8 parts of base. In the following table, find the parts of base that need to be added.

Solution:
Let the number to be filled in the blanks be a, b, c and d respectively.

Ex 13.1 Class 8 Maths

Question 3.
In Question 2 above, if 1 part of a red pigment requires 75 mL of base, how much red pigment should we mix with 1800 mL of base?
Solution:
Let the required red pigment be x part.

Hence, the required amount of red pigment = 24 parts.

               

 

 

 

 

 

Ex 13.1 Class 8 Maths 

Question 4.
A machine in a soft drink factory fills 840 bottles in six hours. How many bottles will it fill in five hours?

Solution:
Let the required number of bottles be x.

Hence the required number of bottles = 700.

Ex 13.1 Class 8 Maths 

Question 5.
A photograph of a bacteria enlarged 50,000 times attains a length of 5 cm as shown in the diagram. What is the actual length of the bacteria? If the photograph is enlarged 20,000 times only, what would be its enlarged length?

Solution:
Let the actual length be x cm.

Ex 13.1 Class 8 Maths

Question 6.
In a model of a ship, the mast is 9 cm high, while the mast of the actual ship is 12 m high. If the length of the ship is 28 m, how long is the model ship?

Solution:
Let the required length of the model ship be x m.

Ex 13.1 Class 8 Maths 

Question 7.
Suppose 2 kg of sugar contains 9 × 10⁶ crystals. How many sugar crystals are there in
(i) 5 kg of sugar?
(ii) 1.2 kg of sugar?

Solution:
Let x be the number of sugar crystals needed.

Ex 13.1 Class 8 Maths 

Question 8.
Rashmi has a road map with a scale of 1 cm representing 18 km. She drives on a road of 72 km. What would be her distance covered in the map?

Solution:
Let the required distance be x km.

Hence the distance covered in the map = 4 cm.

Ex 13.1 Class 8 Maths 

Question 9.
A 5 m 60 cm high vertical pole casts a shadow 3 m 20 cm long. Find at the same time
(i) the length of the shadow cast by another pole 10 m 50 cm high,
(ii) the height of a pole which casts a shadow 5 m long.

Solution:
(i) Let the required length of shadow be x m.

Ex 13.1 Class 8 Maths 

Question 10.
A loaded truck travels 14 km in 25 minutes. If the speed remains the same, how far can it travel in 5 hours?

Solution:
Let the required distance be x km.

Hence the required distance = 168 km.