# Lesson 3

Hello again.  Hope you've had a good day yesterday.

Today's Maths is about finding the complement number.  This means the number that goes with another to create a whole number.  Yes the language is a bit confusing but it essentially means the number bond: a pair of numbers to make another number.   So the number that complements 4 to make 10 is 6.  4 + 6 = 10.

We will be looking a two digit numbers today.  So the complement number to 32 to make 40 is 8.  32 + 8 = 40.

Use the question sheet below and fill in the missing number.    Think about how you will answer these question.  Will you count on from the given number to the answer.  Or would you count backwards from the answer to the first number to find that missing number.

## Printable find the missing number

Find the inverse for each question.   Inverse means the opposite action.  For example question one is 47 + ? = 50.   Opposite to addition is subtraction.

You will write:

The answer is            47 + 3 = 50

The inverse is            50 - 47 = 3

To understand that to find the "Difference" between two numbers is subtraction.

For example:

What is the difference between 65 and 42?

As a number sentence this is written as 65 - 42 = 23

Using your number cards create two 2-digit numbers.  Write in words or say a difference question for your numbers.

For example:  I chose the numbers 42 and 53. I would then write or say "What is the difference between 42 and 53?   REMEMBER when we are subtracting we ALWAYS write the largest number first.

So your number sentence will be      53 - 42 = ?

Use your number knowledge to work out the answer.  If you want to break it down into tens and ones like we did last week please do that.

53 - 42 =

50 - 40 = 10

3 - 2 = 1

10 + 1 = 11

True or False....... EXPLAIN your answers in words either written or tell someone.

1. The difference between 80 and 69 is 22.
2. The difference between 43 and 63 is 20
3. The difference between 23 and 70 is 60
4. The difference between 21 and 62 is 41
5. If the difference is 17, what could be two numbers am I the difference between?   Is there only one answer for this question? How many can you find?

Remember to explain exactly how it is True or False.  e.g.  I know that ...... There are ... tens and ... ones in this number.  I can see the ones in this number are less than the ones in the other number.

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