Number facts

You need to know your number bonds to 20.

These are all addition facts to 20, and from these you can learn the subtraction facts.

For example:

7 + 8 = 15 and 15 – 8 = 7

Learn these and then use them to help you with trickier sums

3 + 9 = 12

9 + 3 = 12

12 – 3 = 9

12 – 9 = 3

Number bonds to 20

Circle 10 pairs of numbers that total 20. The pairs of numbers must be touching, wither horizontally, vertically or diagonally.

One has been done for you.

4 7 1 19 10 11

16 12 10 13 8 9

3 10 0 16 6 14

5 4 2 9 12 10

3 17 15 18 5 8

6 7 13 1 15 2

+ 0 1 2 3 4 5 6 7 8 9 10

0 0 1 2 3 4 5 6 7 8 9 10

1 1 2 3 4 5 6 7 8 9 10

11

2 2 3 4 5 6 7 8 9 10

11

12

3 3 4 5 6 7 8 9 10

11

12

13

4 4 5 6 7 8 9 10

11

12

13

14

5 5 6 7 8 9 10

11

12

13

14

15

6 6 7 8 9 10

11

12

13

14

15

16

7 7 8 9 10

11

12

13

14

15

16

17

8 8 9 10

11

12

13

14

15

16

17

18

9 9 10

11

12

13

14

15

16

17

18

19

10

10

11

12

13

14

15

16

17

18

19

20

RoundingIf you need to add or take away 9 or 19, round the

number to 10 or 20 to make it easier

Examples:16 + 9 37 + 19 34 - 9 63 - 19

Add 10, Add 20, Take away 10, Take away 20,

take away 1 take away 1 add 1 add 1

Answer: 25 Answer: 56 Answer: 25 Answer: 44

You can also use this method to add or take away larger numbers ending in 9 such as 29, 29 and 49

Adding 2-digit numbersIf you know your number bonds, then adding

bigger numbers in you head is easier.

Example:

35 + 57 Use these three steps:

1. Hold the bigger number in your head: 57

2. Add the tens: 57 + 30 = 87

3. Add the units: 87 = 5 = 92

Complete activity sheets 3.2 and 3.3

Subtracting 2-digit numbers

A really good method for subtraction is to find the difference between he numbers by counting

on.

Example:

93 – 56 This number line shows exactly what goes on in your head

56 60 93

Count on from 56 to 60. Hold the 4 in your head.

60 to 93 is 33 33 + 4 is 37 so 93 – 56 = 37

If it helps, draw a number line. Remember to put the smaller number on the left and the larger number on the right

Mental calculationsCalculate the answers and use the code to crack the code:

34 + 16 = 50 A

53 + 19 =

27 + 23 =

32 + 9 =

46 + 45 =

17 + 28 =

91 – 19 =

78 – 28 =

54 – 9 =

63 – 22 =

82 – 77 =

65 – 49 =

91 = H

45 = S

50 = A

16 = R

72 = M

41 = T

5 = E

Written additionIf you are given a sum and the numbers are too big, or there are too many numbers to add in your head, then you need to use a written method.

Follow this step-by-step method:

1. Write the numbers neatly in a column, lining up the digits

2. Start by adding from the right-hand column. For any total over 9 just put the tens digit under the next column

3. Now do the same with the tens column. Keep going left until all the columns have been added.

3527

+768

____

3527

+768

___5

1

3527

+768

4295

1 1

Calculate the answers.

8012 5647 3390

+1579 +3528+4691

_____ _____ _____

Use the written method to calculate these answers:

37.21 + 16.95 2755 + 346 28.09 + 4.98

When you add decimals, remember to line up the decimal point.

Written subtractionHere are two good ways to subtract. Have a go at both methods and choose the one that you feel happier with.

Method 1

1. Write the numbers in a column, lining up the units digits

2. Start from the right-hand column, take away the bottom number from the top number.

3. Now do the same with the other columns. If the top number is smaller than the bottom number, then, in this example, exchange a 100 from the hundreds column. You are making the 40 into 140 and the 300 into 200

346

- 84

____

346

- 84

2

2 14

346 2146

- 84 - 84

____ 262

Method 2

Find the difference between the numbers by counting on.

1. Draw a blank number line

84 3462. Count on to the next ten, then to the next hundred, then to the number

84 90 100 346

6 10246

3. Add up all the jumps. 246 + 10 + 6 = 262

Calculate the answers.

7461 9625 5330

- 831 - 2459 -1822

_____ _____ _____

Use the written method to calculate these answers:

63.18 – 45.02 = 4829 – 764 = 13.5 – 9.62 =

When you take away decimals, remember to line up the decimal point.

Try these using any of the above methods:

1. 345 + 267 6. 709 + 426

2. 1485 + 2097 7. 1268 + 691

3. 862 + 28 8. 486 – 127

4. 506 – 329 9. 865 – 426

5. 259 – 102 10. 682 - 327

Word problemsAnswer these questions.

1. Meera has saved £27 and has £28 birthday money. She wants to buy a bike for £72. How much money does she still need before she can buy the bike?

2. A tourist bus travelled 147km to London, 16km around the sights of London and then 147km back home. How far did the bus travel in total?

3. Tom’s Gran is 84 years old. His Mum is 35 years younger than his Gran and Tom is 38 years younger than his Mum. How old is Tom?

4. A library needs a bookshelf 2.53 m long and they have two shelves, 1.48m and 1.7m in length. How much will have to be cut off one of the shelves to make them fit?