#### Chapters

Chapter 2: Exponents

Chapter 3: Squares and Square Root

Chapter 4: Cubes and Cube Roots

Chapter 5: Playing with Numbers

Chapter 6: Sets

Chapter 7: Percent and Percentage

Chapter 8: Profit, Loss and Discount

Chapter 9: Interest

Chapter 10: Direct and Inverse Variations

Chapter 11: Algebraic Expressions

Chapter 12: Identities

Chapter 13: Factorisation

Chapter 14: Linear Equations in one Variable

Chapter 15: Linear Inequations

Chapter 16: Understanding Shapes

Chapter 17: Special Types of Quadrilaterals

Chapter 18: Constructions

Chapter 19: Representing 3-D in 2-D

Chapter 20: Area of a Trapezium and a Polygon

Chapter 21: Surface Area, Volume and Capacity

Chapter 22: Data Handling

Chapter 23: Probability

## Chapter 10: Direct and Inverse Variations

### Selina solutions for Concise Mathematics Class 8 ICSE Chapter 10 Direct and Inverse Variations Exercise 10 (A) [Pages 120 - 121]

**In which of the following table, x and y vary directly:**

x | 3 | 5 | 8 | 11 |

y | 4.5 | 7.5 | 12 | 16.5 |

**In which of the following table, x and y vary directly:**

x | 16 | 30 | 40 | 56 |

y | 32 | 60 | 80 | 84 |

**In which of the following table, x and y vary directly:**

x | 27 | 45 | 54 | 75 |

y | 81 | 180 | 216 | 225 |

**If x and y vary directly, find the values of x, y, and z:**

x | 3 | x | y | 10 |

y | 36 | 60 | 96 | z |

A truck consumes 28 litres of diesel for moving through a distance of 448 km. How much distance will it cover in 64 litres of diesel?

For 100 km, a taxi charges ₹ 1,800. How much will it charge for a journey of 120 km?

If 27 identical articles cost ₹ 1,890, how many articles can be bought for ₹ 1,750?

7 kg of rice costs ₹ 1,120. How much rice can be bought for ₹ 3,680?

6 note-books cost ₹ 156, find the cost of 54 such note-books.

22 men can dig a 27 m long trench in one day. How many men should be employed for digging 135 m long trench of the same type in one day?

If the total weight of 11 identical articles is 77 kg, how many articles of the same type would weigh 224 kg?

A train is moving with a uniform speed of 120 km per hour.**(i) **How far will it travel in 36 minutes?**(ii)** In how much time will it cover 210 km?

### Selina solutions for Concise Mathematics Class 8 ICSE Chapter 10 Direct and Inverse Variations Exercise 10 (B) [Page 123]

**Check whether x and y vary inversely or not.**

x |
4 | 3 | 12 | 1 |

y |
6 | 8 | 2 | 24 |

**Check whether x and y vary inversely or not.**

x |
30 | 120 | 60 | 24 |

y |
60 | 30 | 30 | 75 |

**Check whether x and y vary inversely or not.**

x |
10 | 30 | 60 | 10 |

y |
90 | 30 | 20 | 90 |

**If x and y vary inversely, find the values of l, m, and n :**

x |
4 | 8 | 2 | 32 |

y |
4 | l | m | n |

**If x and y vary inversely, find the values of l, m, and n :**

x |
24 | 32 | m | 16 |

y |
l | 12 | 8 | n |

36 men can do a piece of work in 7 days. How many men will do the same work in 42 days?

12 pipes, all of the same size, fill a tank in 42 minutes. How long will it take to fill the same tank, if 21 pipes of the same size are used?

In a fort 150 men had provisions for 45 days. After 10 days, 25 men left the fort. How long would the food last at the same rate?

72 men do a piece of work in 25 days. In how many days will 30 men do the same work?

If 56 workers can build a wall in 180 hours, how many workers will be required to do the same work in 70 hours?

A car takes 6 hours to reach a destination by travelling at a speed of 50 km per hour. How long will it take when the car travels at a speed of 75 km per hour?

### Selina solutions for Concise Mathematics Class 8 ICSE Chapter 10 Direct and Inverse Variations Exercise 10 (C) [Pages 125 - 126]

Cost of 24 identical articles is Rs. 108, Find the cost of 40 similar articles.

If 15 men can complete a piece of work in 30 days, in how many days will 18 men complete it?

In order to complete a work in 28 days, 60 men are required. How many men will be required if the same work is to be completed in 40 days?

A fort had provisions for 450 soldiers for 40 days. After 10 days, 90 more soldiers come to the fort. Find in how many days will the remaining provisions last at the same rate?

A garrison has sufficient provisions for 480 men for 12 days. If the number of men is reduced by 160; find how long will the provisions last?

`3/5` quintal of wheat costs Rs.210. Find the cost of :**(i)** 1 quintal of wheat**(ii)** 0.4 quintal of wheat

If `2/9` of property costs Rs.2,52,000; find the cost of `4/7` of it.

4 men or 6 women earn Rs. 360 in one day. Find, how much will:**(i)** a man earn in one day?**(ii)** a woman earn in one day?**(iii)** 6 men and 4 women earn in one day?

16 boys went to the canteen to have tea and snacks together. The bill amounted to Rs. 114.40. What will be the contribution of a boy who pays for himself and 5 others?

50 labourers can dig a pond in 16 days. How many labourers will be required to dig another pond, double in size in 20 days?

If 12 men or 18 women can complete a piece of work in 7 days, in how many days can 4 men and 8 women complete the same work?

If 3 men or 6 boys can finish a work in 20 days, how long will 4 men and 12 boys take to finish the same work?

A particular work can be completed by 6 men and 6 women in 24 days; whereas the same work can be completed by 8 men and 12 women in 15 days. Find :**(i) **according to the amount of work done, one man is equivalent to how many women.**(ii) **the time is taken by 4 men and 6 women to complete the same work.

If 12 men and 16 boys can do a piece of work in 5 days and, 13 men and 24 boys can do it in 4 days, how long will 7 men and 10 boys take to do it?

### Selina solutions for Concise Mathematics Class 8 ICSE Chapter 10 Direct and Inverse Variations Exercise 10 (D) [Pages 129 - 130]

Eight oranges can be bought for Rs. 10.40. How many more can be bought for Rs.16.90?

Fifteen men can build a wall in 60 days. How many more men are required to build another wall of the same size in 45 days?

Six taps can fill an empty cistern in 8 hours. How much more time will be taken, if two taps go out of order? Assume, all the taps supply water at the same rate.

A contractor undertakes to dig a canal, 6 kilometers long, in 35 days and employed 90 men. He finds that after 20 days only 2 km of the canal has been completed. How many more men must be employed to finish the work on time?

If 10 horses consume 18 bushels in 36 days. How long will 24 bushels last for 30 horses?

A family of 5 persons can be maintained for 20 days with Rs.2,480. Find, how long Rs.6944 maintains a family of 8 persons?

90 men can complete a work in 24 days working 8 hours a day. How many men are required to complete the same work in 18 days working `7 1/2` hours a day?

Twelve typists, all working with the same speed, type a certain number of pages in 18 days working 8 hours a day. Find, how many hours per day must sixteen typists work in order to type the same number of pages in 9 days?

If 25 horses consume 18 quintal in 36 days, how long will 28 quintal last for 30 horses?

If 70 men dig 15,000 sq. m of a field in 5 days, how many men will dig 22,500 sq. m field in 25 days?

A contractor undertakes to build a wall 1000 m long in 50 days. He employs 56 men, but at the end of 27 days, he finds that only 448 m of the wall is built. How many extra men must the contractor employ so that the wall is completed in time?

A group of labourers promises to do a piece of work in 10 days, but five of them become absent. If the remaining labourers complete the work in 12 days, find their original number in the group.

Ten men, working for 6 days of 10 hours each, finish `5/21` of a piece of work. How many men working at the same rate and for the same number of hours each day, will be required to complete the remaining work in 8 days?

### Selina solutions for Concise Mathematics Class 8 ICSE Chapter 10 Direct and Inverse Variations Exercise 10 (E) [Page 133]

A can do a piece of work in 10 days and B in 15 days. How long will they take together to finish it?

A and B together can do a piece of work in `6 2/3` days, but B alone can do it in 10 days. How long will A take to do it alone?

A can do a work in 15 days and B in 20 days. If they together work on it for 4 days; what fraction of the work will be left?

A, B, and C can do a piece of work in 6 days, 12 days, and 24 days respectively. In what time will they altogether do it?

A and B working together can mow a field in 56 days and with the help of C, they could have mowed it in 42 days. How long would C take by himself?

A can do a piece of work in 24 days, A and B can do it in 16 days and A, B, and C in `10 2/3` days. In how many days can A and C do it working together?

A can do a piece of work in 20 days and B in 15 days. They worked together on it for 6 days and then A left. How long will B take to finish the remaining work?

A can finish a piece of work in 15 days and B can do it in 10 days. They worked together for 2 days and then B goes away. In how many days will A finish the remaining work?

A can do a piece of work in 10 days; B in 18 days; and A, B, and C together in 4 days. In what time would C alone do it?

A can-do `1/4` of work in 5 days and B can do `1/3` of the same work in 10 days. Find the number of days in which both working together will complete the work.

One tap can fill a cistern in 3 hours and the waste pipe can empty the full cistern in 5 hours. In what time will the empty cistern be full, if the tap and the waste pipe are kept open together?

A and B can do a work in 8 days; B and C in 12 days, and A and C in 16 days. In what time could they do it, all working together?

A and B complete a piece of work in 24 days. B and C do the same work in 36 days; and A, B, and C together finish it in 18 days. In how many days will:**(i) **A alone,**(ii) **C alone,**(iii)** A and C together, complete the work?

A and B can do a piece of work in 40 days; B and C in 30 days; and C and A in 24 days.**(i) **How long will it take them to do the work together?**(ii)** In what time can each finish it working alone?

A can do a piece of work in 10 days, B in 12 days, and C in 15 days. All begin together but A leaves the work after 2 days and B leaves 3 days before the work is finished. How long did the work last?

Two pipes P and Q would fill an empty cistern in 24 minutes and 32 minutes respectively. Both the pipes being opened together, find when the first pipe must be turned off so that the empty cistern maybe just filled in 16 minutes.

## Chapter 10: Direct and Inverse Variations

## Selina solutions for Concise Mathematics Class 8 ICSE chapter 10 - Direct and Inverse Variations

Selina solutions for Concise Mathematics Class 8 ICSE chapter 10 (Direct and Inverse Variations) include all questions with solution and detail explanation. This will clear students doubts about any question and improve application skills while preparing for board exams. The detailed, step-by-step solutions will help you understand the concepts better and clear your confusions, if any. Shaalaa.com has the CISCE Concise Mathematics Class 8 ICSE solutions in a manner that help students grasp basic concepts better and faster.

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Concepts covered in Concise Mathematics Class 8 ICSE chapter 10 Direct and Inverse Variations are Variations, Types of Variation, Direct Variation, Inverse Variation, Concept for Unitary Method (With Only Direct Variation Implied), Concept of Arrow Method, Time and Work.

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