# MATHEMATICS IV

## Solutions Chapter 6 – The Junk Seller

#### Question 1:

• What about you? Do you also find Maths difficult? • What is the most difficult thing in your Maths books? ________ • What do you think is the easiest lesson? ________

Disclaimer: The answer may vary from student to student based on his/her experience. It is highly recommended that the students prepare the answers on their own.

#### Question 1:

Find out: how much for  a cup of tea?

Ask people and find out the cost of a cup of tea • at a tea stall ____________ • at a hotel _______________

Disclaimer: The purpose of this section is to make the students observe their surroundings. The answer may vary from student to student based on his/her experience. It is highly recommended that the students prepare the answers on their own.

#### Question 2:

If a person who runs a tea stall earns Rs 30 in a day, how much will he earn in 10 days? _____________

And in a month? _______________ How did you get the answer? Discuss.

Earning of the man in 1 day = Rs 30 Earning of the man in 10 days = Rs 30 × 10 = Rs 300

We do it in the following manner:

1 times 30 is 30. 10 times 30 is 300.

Suppose there are 30 days in a month. Earning of the man in a month or 30 days = Rs 30 × 30 = Rs 900 We do it in the following manner: 3 times 30 is 90. 30 times 30 is 900.

#### Question 3:

Hariya and Babu want to buy a handcart for Rs 300. Who has to pay back more — Hariya or Babu? _____________

Hariya took a loan of Rs 300 from a bank for 6 months to buy a handcart. He pays Rs 51 every month to the bank. Money paid back by Hariya to the bank in 1 month = Rs 51 Money paid back by Hariya to the bank in 6 months = Rs 51 × 6 = Rs 306

We do it in the following manner: 6

×50 = 300 6

×1 = 6 So,

300+6306 So, Hariya paid Rs 306 to the bank after 6 months.

Babu took a loan of Rs 300 from Chunnilal for 6 months to buy a handcart. He paid Rs 360 to Chunnilal after 6 months. Thus, Babu has to pay back more than Hariya for buying the handcart.

#### Question 1:

I have 9 rickshaws of my own. I give the rickshaws on rent. each for Rs 20 a day. On Sundays I do not take any money for them. • In a week how much does Kiran earn from one rickshaw?

We know that there are 7 days in a week. Earning of Kiran from 1 rickshaw per day = Rs 20 Earning of Kiran from 1 rickshaw for 7 days = Rs 20 × 7 = Rs 140

We do it in the following manner: 2 times 7 is 14. 20 times 7 is 140.

Now, On Sunday, Kiran does not take any money for the rickshaws. Therefore, earning of Kiran from 1 rickshaw for 6 days = Rs 140 − Rs 20 = Rs 120 We do it in the following manner:

140-20120¯So, Kiran will earn Rs 120 in a week from 1 rickshaw.

#### Question 1:

Do it mentally and write the answers.

• 2 × 6 = __________
• 20 × 6 = __________
• 2 × 60 = __________
• 3 × 42 = __________
• 4 × 80 = __________
• 4 × 81 = __________
• 9 × 25 = __________
• 31 × 9 = __________

• 12
• 120

We do it in the following manner: 2 times 6 is 12. 20 times 6 is 120.

• 120
• 126

We do it in the following manner: 3

×40 = 120 Also, 3

×2 = 6 So, 120+6126¯

• 320

We do it in the following manner: 4 times 8 is 32. 4 times 80 is 320.

• 324

We do it in the following manner: 4

×80 = 320 Also, 4

×1 = 4 So, 320+4324¯

• 225

We do it in the following manner: 9

×20 = 180 Also, 9

×5 = 45 So, 1180+45225¯

• 279

We do it in the following manner: 30

×9 = 270 Also, 1

×9 = 9 So, 270+09279¯

#### Question 2:

Look up the rate list to see today’s rates. Help Kiran to find out the cost of the junk. • How much will Kiran pay for 31 kg newspaper? 1 kg newspaper costs Rs 5. 30 kg cost Rs 5 × 30 = Rs 150. So for 31 kg she pays Rs _____. • How much will Kiran pay for 42 kg newspaper? • Also find the cost of: (a) 22 kg of plastic (b) 23 kg of waste paper (c) 12 kg of iron

 Rate-List Kind of Junk Price of 1 Kg 1. Waste Paper Rs 4/- 2. Newspaper Rs 5/- 3. Iron Rs 12/- 4. Brass Rs 170/- 5. Plastic Rs 10/-

Can you do this without writing? Guess the total money Kiran will pay to the junk collectors. Will it be — More than 600? — Less than 600?

• Cost of 1 kg newspaper = Rs 5

Cost of 31 kg newspaper = Rs 5 × 31 = Rs 155

We do it in the following manner: 5 × 30 = 150 5 × 1 = 5 So, 150+5155

• Cost of 42 kg newspaper = Rs 5 × 42

= Rs 210 We do it like this: 5 × 40 = 200 5 × 2 = 10 So, 200+10210   (a) Cost of 1 kg plastic = Rs 10 Cost of 22 kg plastic = 22 × Rs 10 = Rs 220

We do it in the following manner: 22 × 1 = 22 22 × 10 = 220

(b) Cost of 1 kg waste paper = Rs 4 Cost of 23 kg wastepaper = Rs 4 × 23 = Rs 92

We do it in the following manner: 4 × 20 = 80 4 × 3 = 12 So, 80+1292(c) Cost of 1 kg iron = Rs 12 Cost of 12 kg iron = Rs 12 × 12 = Rs 144

We do it in the following manner: Add the numbers in the box

1002020+4144Total money paid to junk collectors will be = Rs 155 + Rs 210 + Rs 220 + Rs 92 + Rs 144 = Rs 821

1251521022092+144821So, the total money paid to the junk seller is more than Rs 600.

#### Question 1:

• Kiran bought 1 kg plastic for Rs 10, but sold 1 kg plastic for Rs 12. How much money does she earn on selling 1 kg plastic? Rs _______ So, how much money does she earn for 63 kg? Rs _______

Cost price of 1 kg plastic = Rs 10 Selling price of 1 kg plastic = Rs 12 Profit on selling 1 kg plastic = Rs (12 − 10) = Rs 2 Profit on selling 63 kg plastic = Rs 2 × 63 = Rs 126

We do it in the following manner: 2 × 60 = 120 2 × 3 = 6

120+6126Hence, Kiran will earn Rs 126 on selling 63 kg plastic.

#### Question 1:

• How much money will Dinu pay for 32 kg iron? • Kiran buys 1 kg iron for Rs 12 but sells it for Rs 14. How much does she earn when she sells 32 kg iron? Rs _______

• Cost of 1 kg iron = Rs 14 Cost of 32 kg iron = Rs 14 × 32 = Rs 448 We do it like this: Add the numbers in the box

30012020+8448So, Dinu will have to pay Rs 448 for 32 kg iron.

• Cost of 1 kg iron for Kiran = Rs 12

Selling price of 1 kg iron = Rs 14 Profit on selling 1 kg iron = Rs (14 − 12) = Rs 2 Profit on selling of 32 kg iron = Rs 2 × 32 = Rs 64

We do it in the following manner: 2 × 30 = 60 2 × 2 = 4

So, 60+464

Thus, Kiran earns Rs 64 on selling 32 kg iron.

#### Question 2:

I bought 1 kg newspaper for Rs 5, but sold it for Rs 6. How much money did I earn by selling 152 kg of newspaper? ________

Cost of 1 kg newspaper = Rs 5 Selling price of 1 kg newspaper = Rs 6 Profit on selling 1 kg newspaper = Rs (6 − 5) = Re 1 Profit on selling 152 kg newspaper = Re 1 × 152 = Rs 152 I earned Rs 152 on selling 152 kg of newspaper.

#### Question 3:

How much money will Dinu pay for 4 kg brass? _________ Guess the answer first.

Cost of 1 kg brass = Rs 180 Cost of 4 kg brass = Rs 4×180 = Rs 720 We will do it as follows: Add the numbers in the box

400+320720Thus, Dinu will pay Rs 720 for 4 kg brass.

#### Question 1:

First guess the answer and then calculate: (a) 37 × 18 = (b) 45 × 24 = (c) 69 × 52 = (d) 77 × 55 = (e) 142 × 5 = (f) 382 × 3 = (g) 2 × 175 = (h) 4 × 206 =

(a) Add the numbers in the box

30024070+56666(b) Add the numbers in the box

800100160+201080

(c) Add the numbers in the box

3000450120+183588

(d) Add the numbers in the box

315100350350+354235

(e) Add the numbers in the box

500200+10710(f) Add the numbers in the box

900240+61146(g). Add the numbers in the box

200140+10350(h) 800+24824

#### Question 1:

Later she paid Rs 919 to the junk collectors. When she sold the junk she got these notes and coins from Dinu. Now you make a record in her diary. Find out how much she earned this time.  We do it as follows:

5 notes of 100 rupee 5

×100 = Rs 500

1 note of 50 rupee 1

×50 = Rs 50

18 notes of 10 rupee 18

×1 = 18 18

×10 = Rs 180

9 notes of 20 rupee 9

×2 = 18 9

×20 = Rs 180

28 coins of 5 rupee 20

×5 = 100 8

×5 = 40

100+4014028

×5 = Rs 140

Money I got = Rs 500 + Rs 50 + Rs 180 + Rs 180 + Rs 140 = Rs 1050

520050180180+1401050Money I earned = Rs 1050 − Rs 919 = Rs 131

10015401-9190131