BODMAS as a first lesson
3 + 2 * 4 = 20
Most people agree with this statement although a few will say the answer is 11. I teach the convention of sequence of operations early in maths courses above level 1 (GCSE Intermediate and Access courses) as a lead into algebra. I use two activities - traditional worksheet and open ended group work.
Just in case you have not heard the mnemonic...
- Brackets
- Operation (some say 'of' meaning multiply - the vowel is here to make a word. You can use the letter i for index, but I don't have the money to keep on registering domain names :- )
- Divide
- Multiply
- Add
- Subtract
- put 3 + 2 * 4 or similar on board
- write = 20 and ask for votes - most will agree
- write = 11 and ask for votes - a few hands will go up and some people will remember
- what are we to do - how can there be two answers in Maths?
- explain the convention that we do multiplication first, addition second.
- ask how can I make 3 + 2 * 4 = 20 true? Someone will remember brackets.
- introduce the mnemonic
- use a worksheet with about 40 questions covering all the types including 4(10-7) = 12 and 15 / 5 + 12 / 6 = 5 and worked examples at the top and answers at the bottom
- explain the layout of the worksheet carefully pointing to all the sections (this lesson is about conventions right?)
- run through the worked examples one by one always relating them to the BODMAS mnemonic
- invite students to work through the worksheet and I always point out the large table square poster we have in the classroom
- move about making sure people are checking off against the BODMAS rules and re-explaining where necessary
4 - 4 + 4 - 4 = 0
Can you find other bodmas expressions that use the number 4 exactly 4 times and make 1, 2, 3, 4, 5, 6, 7, 8, 9??
- Work in groups
- What can you make with just two 4s?
- introduce by asking for expressions that make (say) 7 - get the idea that now we have the answer but need the question
- what can you make with two 4s? (4 * 4, 4 + 4, 4 - 4, 4 + 4)
- invite students to work in groups of three or four. People will ask for clarification of the task
- circulate prompting the groups to play with combinations of the two fours, or to just take some scrap paper and write 4 down four times and stick operations between them and see what happens. Avoid people sitting there staring at a list of the numbers 0 to 9
- After about 20 minutes most groups will be getting there - 6 and 8 are difficult to find. Many groups suss that 7 and 9 are related and 3 and 5 are related. I sometimes remind people that 2 is 1 + 1
- Feedback onto a prepared flipchart or board display. Ask who has one, and so on, going through the expressions and inviting the whole group to check
- Congratulate groups on completing a difficult task and invite views on the strategy they used and their roles in the group
- ask people how the activities were different
- which one was more fun?
- could they have done the group work without the skills base provided by the first activity?
- which activity was more interesting? Any ideas why?
Originally added on Monday, March 31, 03
in category: number
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