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Numeracy Support: Written Calculations

Mawdesley St Peter’s. Numeracy Support: Written Calculations. When do we use written calculations?. Written calculation methods are an important skill that children need to learn, and are practised frequently in school.

yvonne-austin
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Numeracy Support: Written Calculations

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  1. Mawdesley St Peter’s Numeracy Support: Written Calculations

  2. When do we use written calculations? • Written calculation methods are an important skill that children need to learn, and are practised frequently in school. • However, there is also a great emphasis on developing the ability to calculate mentally and for children to choose a method which suits them. • The important thing when supporting written calculations is that children understand what they are doing.

  3. Written or Mental Method? • Depends on the situation e.g. Are we solving word problems or doing a mental maths test? Would we need to be able to calculate mentally e.g. working out change when buying something in a shop? • What do we notice about the numbers- are they close to one another? Are there any number bonds to help us? • 13 + 17= • 25 x 12= • 356 - 148= • 245 x 16= • 189 – 99=

  4. Written Methods for Multiplication • In our school, we use a written method for multiplication which we call the ‘grid method’. • Let’s try 56 x 7. • 56 can be partitioned into 50 and 6. • 7 can’t be partitioned as it contains only units.

  5. 56 x 7=

  6. 56 x 7=

  7. 56 x 7= • Next, we would add 350 and 42 to get the answer. • This could be done mentally i.e. 350 + 40 + 2= 392 • Or it could be added using a written method i.e. 350 + 42 392

  8. This method works with bigger numbers too... • 146 x 28=

  9. Then add the numbers together to get your answer. 2000 + 800 + 120= 2920 800+ 320 + 48= + 1168 4088 So 146 x 28= 4088

  10. With decimals.. • 34.6 x 6= • 180 + 24 + 3.6= 207.6

  11. With money... • £6.65 x 7= • £42 + £4.20 + 35p= £46.55

  12. Common Errors • Incorrect partitioning E.g. 56 into 5 and 6 rather than 50 and 6. • Errors in multiplication E.g. times tables mistakes and ‘forgetting 0s’

  13. Why do we use this method? • Children understand the steps that they are taking to get to the answer. • Drawing a grid means that children will not miss out a step as all the boxes have to be filled. • Easier for adults to see where they have made errors.

  14. Written Methods for Division • To divide by a single digit number, we use a traditional short division method. 72 ÷3=

  15. Division by chunking • Also known as repeated subtraction. • We this method for larger numbers e.g. Dividing by a 2 digit number. • Let’s look at a division problem...

  16. 384 / 24= • 384 children in a school are put into groups of 24. How many groups would there be altogether? • We work out how many groups of 24 there are in 384.

  17. 384÷24= How many 24s go into 384? 24 384 - 240 (10 x 24) 144 - 120 ( 5x 24) 24 - 24 (1x 24) 0 Finally, add up how many lots of 24 you have taken away ( 10 + 5 + 1 = 16) and you have an answer. There would be 16 groups of children.

  18. Lets try 317 ÷ 12 12 317 -120 (10 x 12) 197 -120 (10 x 12) 77 - 60 (5 x 12) 17 - 12 ( 1 x 12) 5 Add the number of times you have taken away 12 ( 10 + 10 + 5 + 1= 26). 5 is the remainder so than answer to 317 ÷ 12= 26 r 5.

  19. Why do we use this method? • This method can take a while to get the hang of, but once children have grasped it they usually find it easy to use. • They understand the steps that they are taking to reach an answer. • Easier than long division and provides an alternative method. • Adults can see what has caused the children to make errors.

  20. Common Errors • Subtraction errors • Forgetting or making mistakes when adding the numbers in brackets.

  21. Addition and Subtraction • Younger children will begin addition by partitioning numbers and adding them • e.g. 43 + 37= 40 + 30 is 70 3 + 7 is 10 70 + 10 is 80.

  22. Addition • Many children continue to use this method for certain calculations as the numbers do not require a written calculation . • However, we do use written methods for addition in school.

  23. Addition 134 + 291= 134 + 291 5 25 425 1

  24. Subtraction • We also use a traditional written subtraction method. • However, children can choose their method depending on the numbers given. • Would 2007- 1994 require a written method? • Most children would use a ‘ counting on’ method for this subtraction.

  25. Subtraction • Let’s try 375- 169 as many children would choose a written method of subtraction for this question. • The only real difference is that we try not to tell children to ‘borrow a 1’. • If we borrow a 1- when is it paid back?? • Instead we tell children to ‘take’ a 10 or 100.

  26. Conclusion • If you have any questions I will stay behind to answer them for you. • Handouts can be kept to refer to if your child is having difficulty with calculations e.g. When doing their homework. • If you would like further support feel free to ask!

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