Multiplication by Multiplication by multiples of 10 and 100multiples of 10 and 100

Objective to multiply numbers Objective to multiply numbers when 0’s are involvedwhen 0’s are involved

StarterStarter

What is the rule for multiplying a What is the rule for multiplying a whole number by 10?whole number by 10?

Write down the number and add a Write down the number and add a zerozero

What is the rule for multiplying a What is the rule for multiplying a whole number by 100?whole number by 100?

Write down the number and add two Write down the number and add two zeroszeros

Calculate the following:Calculate the following:

47 X 1047 X 10 23 X 10023 X 100 16 X 10016 X 100 52 X 1052 X 10 84 X 1084 X 10 79 X 10079 X 100 31 X 10031 X 100 95 X 100095 X 1000 58 X 10,00058 X 10,000

470470 2,3002,300 1,6001,600 520520 840840 7,9007,900 3,1003,100 95,00095,000 580,000580,000

Main ActivityMain Activity

Calculate 30 X 40Calculate 30 X 40 Multiply 3 X 4Multiply 3 X 4 1212 How many zeros in the question?How many zeros in the question? TwoTwo 30 X 40 = 120030 X 40 = 1200 OR 3 X 4 = 12 30 X 4 = 120 so OR 3 X 4 = 12 30 X 4 = 120 so

30 X 40 =120030 X 40 =1200

Another exampleAnother example Calculate 40 X 500Calculate 40 X 500 Multiply 4 by 5Multiply 4 by 5 2020 How many zeros in the question?How many zeros in the question? ThreeThree 40 X 500 = 20,000 40 X 500 = 20,000

Yet another exampleYet another example Calculate 700 X 300Calculate 700 X 300 Multiply 7 by 3Multiply 7 by 3 2121 How many zeros in the question?How many zeros in the question? FourFour 700 X 300 = 210,000700 X 300 = 210,000

Lets check that we understand Lets check that we understand

200 X 70200 X 70 60 X 3060 X 30 800 X 400800 X 400 2,000 X 302,000 X 30

14,00014,000 1,8001,800 320,000320,000 60,00060,000

The rule-plenaryThe rule-plenary

We are to multiply two numbers that We are to multiply two numbers that are multiples of powers of ten are multiples of powers of ten

Firstly we multiply the two digits Firstly we multiply the two digits together ignoring the zerostogether ignoring the zeros

We work out how many zeros in the We work out how many zeros in the questionquestion

We add the number of zeros to our We add the number of zeros to our initial answerinitial answer