Multiplying by powers of 10 Decimals

POWERS of 10 with DECIMALS the decimal point moves to the right while the digits move to the left. 25.9 x 10 = . 2 5 9 Decimal moves 1 place to the right because there is 1 zero . Digits move 1 place to the left because there is 1 zero 2 5 9

Calculate 34.2 x 10 First, look at the number in the place value table... . Now, where does 34.2 belong in this table? 3 4 2 .

. . 3 4 2 . 124 x 10 Multiplying by 10 means every digit must move left by 1 column because there is 1 zero . . 3 4 2 Decimal moves one place to the right because there is 1 zero while the digits move to the left. . So now we know that 34.2 x 10 = 342

Calculate 36.94 x 100 First, look at the number in the place value table... . Now, where does 36.94 belong in this table? 3 6 . 9 4

. . 3 6 9 4 . 36.94 x 100 Multiplying by 100 means every digit must move left by 2 columns because there are 2 zeros . . 3 6 9 4 . So now we know that 36.94 x 100 = 3694

. 5 1 2 . 1 Calculate 12.105 x 100 First, draw a place value table... Now, where does 12.105 belong in this table? 5 1 2 . 1

. . 1 2 1 5 . 12.105 x 100 Multiplying by 100 means every digit must move left by 2 columns because there are 2 zeros . . 1 2 1 5 1210.5 . So now we know that 12.105 x 100 =

Remember the rules… What is the rule for multiplying a whole number by 10? Write down the number and add a zero What is the rule for multiplying a whole number by 100? Write down the number and add two zeros TO SUM IT UP – multiply and then add the zeros

Take a look… Calculate 30 X 40 Multiply 3 X 4 = 12 How many zeros in the question? Two 30 X 40 = 1200

Here we go again… Calculate 40 X 500 Multiply 4 by 5 = 20 How many zeros in the question? Three 40 X 500 = 20,000

Your Turn! 46.441 x 10 = 200 x 70= 160 x 100 = 3.2 x 1000 = 12 x 10 = 136 x 10 = 2.2 x 10 = 14.6 x 10 = 120 464.41 14000 1360 16000 22 3200 146

Multiplying by 0.1 and 0.01 What is 4 × 0.1? We can think of this as 4 sets of 0.1 or 0.1 + 0.1 + 0.1 + 0.1. We can also think of this as 4 × 1 10 which is the same as 4 ÷ 10 Therefore, 4 × 0.1 = 0.4 Multiplying by 0.1 Dividing by 10 is the same as **TRICK- 0.1 move the invisible decimal 1 place to the left**

Multiplying by 0.1 and 0.01 What is 3 × 0.01? We can think of this as 3 lots of 0.01 or 0.01 + 0.01 + 0.01. 1 100 We can also think of this as 3 × which is equivalent to 3 ÷ 100 Therefore, 3 × 0.01 = 0.03 Multiplying by 0.01 Dividing by 100 is the same as **TRICK- 0.01 move the invisible decimal 2 place to the left**

Multiplying by 0.1 and 0.01 4 × 0.1 = 0.4 Multiplying by 0.1 Dividing by 10 is the same as **TRICK- 0.1 move the invisible decimal 1 place to the left** 3 × 0.01 = 0.03 Multiplying by 0.01 Dividing by 100 is the same as **TRICK- 0.01 move the invisible decimal 2 place to the left**