Missing-numbers.ppt
- 1. Missing Numbers Today we are going to have another look at missing number problems. We have looked at this with addition and subtraction, but today we are going to cover all four operations.
- 2. Missing Numbers Addition and Subtraction RECAP Let’s remind ourselves of the rhyme we use in school to help us! Missing number at the beginning, Do the inverse and you’re winning We looked at the inverse of addition and subtraction. Addition and subtraction are the opposite of each other. We say that they are inverse operations. ______ + 13 = 36 So, the inverse of addition is subtraction. 36 – 13 = _____ The answer is 23 ______ - 8 = 27 So, the inverse of subtraction is addition. 27 + 8 = _____ The answer is 35
- 3. Missing Numbers Addition and Subtraction RECAP Let’s remind ourselves of the second part of the rhyme we use in school to help us! Missing number in the middle, Do subtraction solve that riddle 24 - _____ = 8 The number is missing from the middle, so we need to do subtraction. 24 – 8 = _____ The answer is 16 Tip – If the missing number is in the middle you must always use subtraction. Only use the inverse when the missing number is at the beginning. That’s why we sing our rhyme so we don’t forget.
- 4. Missing Numbers Multiplication and Division From this array I can write a multiplication sentence. 3 x 4 = I can see 3 lots of 4. I could also write 4 x 3 = It depends which way you look at it, but we know that it doesn’t matter as multiplication can be done in any order and you will always get the same answer.
- 5. Missing Numbers Multiplication and Division Multiplication and division are also inverse operations. Fact families help show the relationship between inverse operations. Example 3 x 4 = 12 12 ÷ 4 = 3 4 x 3 = 12 12 ÷ 3 = 4
- 6. Missing Numbers Multiplication and Division From an array you can write 4 different multiplication and division number sentences. We are using all the number facts we know. - Multiplication can be done in any order (commutative) - Division cannot (Biggest number always goes first) Fact families help show the relationship between inverse operations. Example 2 x 5 = 10 10 ÷ 5 = 2 5 x 2 = 10 10 ÷ 2 = 5
- 7. Missing Numbers Multiplication and Division How do we use this to help us solve missing number problems? Think FACT FAMILIES Example 1 3 x ___ = 15 There are 3 lots of ____ that equal 15. So, 15 ÷ 3 will give me the answer. Work this out using an array. 15 ÷ 3 = 5 Pop your answer back into the missing number problem to check it is correct.
- 8. Missing Numbers Multiplication and Division Example 2 20 ÷ ___ = 4 This tells me there are 20 in total and 4 in each group. So, how many groups of 4 do I need to make 20? 4 x ___ = 20 ‘So’ many lots of 4 = 20 Work this out using an array. The answer is 5.
- 9. Missing Numbers TOP TIPS 1. Read problem carefully and THINK INVERSE 2. - Addition and Subtraction recall rhyme - Multiplication and Division recall fact families 3. Choose method - Addition and Subtraction (column method or tens and ones) - Multiplication and Division (arrays and mental recall of facts) Log on to Purple Mash to complete Task 1 and Task 2. Use paper to do your working out! Good luck with this super challenge!