**Addition and Subtraction to 99**

Bridging to a Multiple of 10AdditionThe bridging to 10 strategy can be used to bridge to numbers that are multiples of 10. This makes it easier to add and subtract numbers mentally. 37 + 8 = ? Step 1: What do we need to add to 37 to get to 40? The answer is 3, so we start by adding 3 of the 8 to get to 40.Step 2: How many more do we need to add? 8 - 3 = 5 so we need to add 5 more: 40 + 5 = 45.So 37 + 8 = 45. Subtraction67 - 9 = ? Step 1: Take 7 from 67 to get to 60.Step 2: Work out how many more to take away: 9 - 7 = 2. We need to take 2 more away: 60 - 2 = 58.So 67 - 9 = 58 |

**Grouping Numbers that Add to 10 or a Multiple of 10**

**Addition**34 + 7 + 6 = ?

Look for best friends that will add to a multiple of 10: 34 + 6 = 40

40 + 7 = 47

So 34 + 7 + 6 = 47

**Subtraction**58 - 13 - 7 = ?

Look for best friends that will add to a multiple of 10: 13 + 7 = 20

58 - 20 = 38

So 58 - 13 - 7 = 38

Inverse StrategyThis strategy turns subtraction into addition. 74 - 56 = ? Step 1: Start with 56. Add to make 60.4Step 2: Add to 60 to make 70.10Step 3: Add to 70 to make 74.4How much have we added altogether? 4 + 10 + 4 = 18 So 74 - 56 = 18 A number line can be used to add and subtract numbers. Go to Jump Strategy to learn more.Jump Strategy |

Using Place ValueSeparate the Tens and OnesAdditionThe tens and ones in the smaller number being added can be separated. 38 + 17 = ? Separate the 10 and 7 in 17. 38 + 10 = 48 48 + 7 = 55 So 38 + 17 = 55 SubtractionThe tens and ones in the number being subtracted can be separated. 84 - 39 = ? Separate the 30 and 9 in 39. 84 - 30 = 54 54 - 9 = 54 - 4 - 5 = 45 So 84 - 39 = 45 |

Split StrategyThe split strategy also uses place value but with this strategy all of the numbers being added or subtracted are split into tens and ones. Addition54 + 44 = ? Separate the tens and ones in both numbers. 54 + 44 = 50 + 4 + 40 + 4 = 50 + 40 + 4 + 4 = 90 + 8 = 98 The split strategy is ideal for and generally used with addition questions in which the tens and ones add to 9 or less but can be used with questions in which you have 10 or more tens or ones. 58 + 69 = ? 58 + 69 = 50 + 8 + 60 + 9 = 50 + 60 + 8 + 9 = 110 + 17 = 127 Subtraction64 - 33 = ? Separate the tens and ones in both numbers. 64 - 33 = 60 - 30 = 30 and 4 - 3 = 1 The answer is 30 and 1 = 31 So 64 - 33 = 31 The split strategy only works well with subtraction questions when the number of tens and ones in the number being taken away is less than the tens and the ones in the number you are taking away from. |

Compensation StrategyThis strategy works well when adding or subtracting numbers that are close to the next multiple of 10. Numbers can be rounded up to the next multiple of 10 so they are easier to work with mentally, you just need to remember to compensate for the rounding up at the end. Addition38 + 19 = ? Round 38 to 40 and subtract 2 at the end. 40 + 19 = 59 - 2 = 57 So 38 + 19 = 57 orRound 19 to 20 and subtract 1 at the end. 38 + 20 = 58 - 1 = 57 You can choose whether you round up the first or second number, if they are both close to the next multiple of 10. |

**Subtraction**38 - 19 = ?

Round 38 to 40 and subtract 2 at the end.

40 - 19 = 21 - 2 = 19

So 38 - 19 = 19

**or**Round 19 to 20 and add 1 at the end (as you will be taking 1 too many away).

38 - 20 = 18 + 1 = 19

You can choose whether you round up the first or second number, if they are both close to the next multiple of 10. If you round the first number up you need to subtract the amount you rounded up by at the end, as you have added that amount to the whole question. If you round up the number you are taking away, you need to add the amount you rounded up by at the end, as you have taken away too many.

Most questions in which the first number is close to a multiple of 10 work best with the split strategy, as the number of tens and ones being taken away in the second number is usually less than in the first number. In our

*Compensation Slideshow*we look only at questions in which we round up the number being subtracted, as these questions most commonly work with this strategy.