The Junk Seller

'Kiran buys old newspapers, iron, plastic, and glass. She weighs them, calculates, and pays the right amount. Multiplication is her superpower!'

1. What You Will Learn

• Multiplication of two-digit and three-digit numbers
• Mental math strategies for multiplication
• Calculating total cost using unit price and quantity
• Understanding profit in buying and selling
• Reading and using a weighing scale

2. Meet Kiran — The Junk Seller

Kiran is a junk seller. She buys old items from people and sells them to a recycling factory. She makes a SMALL profit on each item.

What Kiran Buys

Every day, Kiran weighs the items on her BIG weighing scale. Then she MULTIPLIES to find the total cost.

3. Multiplication in Kiran's Work

Example 1: Buying Newspapers

A customer brings 23 kg of newspapers. How much does Kiran pay?

• Price per kg = ₹6
• Total kg = 23
• Money to pay = 23 × 6 = ?

Step-by-step:

• 20 × 6 = 120
• 3 × 6 = 18
• 120 + 18 = ₹138

Example 2: Buying Iron

Another customer brings 45 kg of iron. How much does Kiran pay?

• Price per kg = ₹12
• Total kg = 45
• Money to pay = 45 × 12 = ?

Step-by-step:

• 45 × 10 = 450
• 45 × 2 = 90
• 450 + 90 = ₹540

4. Mental Math Tricks

Trick 1: Break the Number

Instead of 34 × 7, think: 30 × 7 = 210, 4 × 7 = 28, then 210 + 28 = 238.

Trick 2: Double and Half

For 25 × 8, double 25 to get 50 and half 8 to get 4: 50 × 4 = 200.

Trick 3: Use 10

For 16 × 9, first do 16 × 10 = 160, then subtract 16: 160 - 16 = 144.

Practice These

5. Understanding Profit

Kiran buys items at one price and sells them at a HIGHER price. The DIFFERENCE is her profit.

Example

• Kiran buys 10 kg of plastic at ₹10 per kg. Total cost = ₹100.
• She sells 10 kg of plastic at ₹14 per kg. Total earning = ₹140.
• Her PROFIT = ₹140 - ₹100 = ₹40

Think About This

Why do people sell junk instead of throwing it away? How does recycling help the environment?

6. Key Facts

• Multiplication is REPEATED ADDITION: 6 × 4 = 6 + 6 + 6 + 6 = 24
• When multiplying by a two-digit number, multiply by TENS first, then ONES, then ADD
• In buying and selling: SELLING PRICE - COST PRICE = PROFIT
• Mental math saves TIME in everyday calculations
• We can use DIFFERENT strategies to solve the same problem

7. Common Mistakes

'Do NOT forget to add the carrying-over number when multiplying.' 'Do NOT add the cost when you need to multiply. Read the question carefully.' 'Do NOT forget that profit is SELLING PRICE minus COST PRICE, not the other way around.' 'Do NOT confuse ₹ and paise. 100 paise = ₹1.' 'Do NOT skip the units — always write kg, ₹, or pieces in your answer.'

8. Fun Activity

Be a Junk Seller for a Day

• Make a list of 5 items in your home that can be recycled
• Assign a price per kg to each item
• Ask a family member to be the customer
• Weigh the items (use a kitchen scale or estimate)
• Calculate the total using multiplication

Around Your Home

• Find 5 things made of iron (utensils, gates, tools)
• Find 5 things made of plastic (bottles, buckets, toys)
• Find 5 things made of glass (bottles, windows, mirrors)

9. Self-Test

Q1. Kiran buys 32 kg of newspaper at ₹6 per kg. How much does she pay? Answer: 32 × 6 = (30 × 6) + (2 × 6) = 180 + 12 = ₹192

Q2. A customer brings 18 kg of iron. Kiran pays ₹12 per kg. What is the total cost? Answer: 18 × 12 = (18 × 10) + (18 × 2) = 180 + 36 = ₹216

Q3. Kiran buys brass at ₹170 per kg. She buys 8 kg. How much does she pay? Answer: 8 × 170 = 8 × 100 + 8 × 70 = 800 + 560 = ₹1,360

Q4. Use mental math: 26 × 7 = ? Answer: 20 × 7 = 140, 6 × 7 = 42, 140 + 42 = 182

Q5. Kiran buys 15 kg of plastic at ₹10 per kg. She sells it at ₹14 per kg. What is her profit? Answer: Cost = 15 × 10 = ₹150. Selling = 15 × 14 = ₹210. Profit = 210 - 150 = ₹60

Q6. Fill in the blank: 45 × 6 = (40 × 6) + (___ × 6) Answer: 5

10. Key Vocabulary