**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.

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.

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.

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.

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 × 10 ^{6} 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.

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