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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