Postman Stories for Multiplying Integers

What do you think? Should a check be represented by a positive number, or a negative one?

What do you think? Should a check be represented by a positive number, or a negative one? Should a bill be represented by a positive number, or a negative one?

Remember... Checks are positive numbers. –A check for $3 may be written as 3. Bills are negative numbers. –A bill for $7 may be written as -7.

What do you think? If the postman brings you mail, do you have more mail than before, or less? Should this be a positive number, or a negative one? If the postman takes away mail, do you have more mail than before, or less? Should this be a positive number, or a negative one?

Remember... If the postman brings you mail, it is represented by a positive number. –If he brings you 6 pieces of mail, write 6. If the postman takes away mail, it is represented by a negative number. –If he takes away 10 pieces of mail, write -10.

Let’s practice! Suppose the postman brings you 5 pieces of mail. How would you write this number?

Let’s practice! Suppose the postman brings you 5 pieces of mail. How would you write this number? Suppose each piece of mail was a check for $10. How would you write this number?

Let’s practice! Suppose the postman brings you 5 pieces of mail. How would you write this number? Suppose each piece of mail was a check for $10. How would you write this number? What multiplication problem represents this situation?

Let’s practice! Suppose the postman brings you 5 pieces of mail. How would you write this number? Suppose each piece of mail was a check for $10. How would you write this number? What multiplication problem represents this situation? 5 x 10 = ?

Let’s practice! Suppose the postman brings you 5 pieces of mail. How would you write this number? Suppose each piece of mail was a check for $10. How would you write this number? What multiplication problem represents this situation? 5 x 10 = 50

Check It! 5 x 10 = 50 Does the answer +50 make sense? Did you gain $50 when he brought you 5 checks for $10 each?

Let’s practice! Suppose the postman brings you 5 pieces of mail. How would you write this number? Suppose each piece of mail was a bill for $10. How would you write this number?

Let’s practice! Suppose the postman brings you 5 pieces of mail. How would you write this number? Suppose each piece of mail was a bill for $10. How would you write this number? What multiplication problem is this? What’s the answer to that multiplication problem?

Let’s Practice! The postman brought you 5 pieces of mail. Each piece of mail was a bill for $10. 5 X -10 = -50

Does it make sense? The postman brings you 5 pieces of mail. Each piece of mail is a bill for $10. You lost $50. This is the number -50! Equation: 5 X -10 = -50 You lost $50. This is the number -50!

Let’s Practice When you paid your bills, the postman took away 5 pieces of mail. Each piece of mail was a check for $10. How can we express this mathematically?

Let’s Practice When you paid your bills, the postman took away 5 pieces of mail. Each piece of mail was a check for $10. How can we express this mathematically? (Write an expression!)

Let’s Practice When you paid your bills, the postman took away 5 pieces of mail. Each piece of mail was a check for $10. How can we express this mathematically? (Write an expression!) -5 X 10 = ?

Let’s Practice When you paid your bills, the postman took away 5 pieces of mail. Each piece of mail was a check for $10. Solution: -5 X 10 = -50

Let’s Practice When you paid your bills, the postman took away 5 pieces of mail. Each piece of mail was a check for $10.

Let’s Practice When you paid your bills, the postman took away 5 pieces of mail. Each piece of mail was a check for $10. Write a math problem for this situation and solve it.

Let’s Practice When you paid your bills, the postman took away 5 pieces of mail. Each piece of mail was a check for $ x 10 = -50

Does it make sense? The postman took away 5 pieces of mail. Each piece of mail was a check for $10. Equation: 5 X -10 = -50 You have $50 less than before. This is the answer: -50!

Last Practice It’s time to bill your customers for your business! The postman takes away 5 pieces of mail. Each piece of mail is a bill for $10.

Last Practice It’s time to bill your customers for your business! The postman takes away 5 pieces of mail. Each piece of mail is a bill for $10. Write an equation for this.

Last Practice The postman takes away 5 pieces of mail. Each piece of mail is a bill for $10. Equation: -5 X -10 = 50

Does It Make Sense? The postman takes away 5 pieces of mail. Each piece of mail is a bill for $10. Equation: -5 X -10 = 50 You made $50! That’s why the answer is +50.

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