Quandaries and Queries
  


Name: jessica

Who is asking: Student
Level: Middle

Question:
my mom and I were wondering 2 things.

1. what is the reason for having bedmas.
2. 5+5-4+[6x3-(6+1-3x2) -5+9]



Hi Jessica,

If I ask you to find 2 + 3 6 + 4 then you have to make a decision.

Do you read from left to right, first adding 2 and 3, and get

5 6 + 4 = 30 + 4 = 34? Do you read from right to left, first adding 6 and 4, to get 2 + 3 10 = 2 + 30 = 32? Do you perform the additions first and then the multiplication 5 10 = 50? Do you perform the multiplication first and then the additions 2 + 18 + 4 = 24? Any of these might be considered to be "the right answer".

Faced with this ambiguity, we need to agree on a procedure so that we all calculate 2 + 3  6 + 4 the same way. The agreeded on "rule" is that you multiply and divide before you add and subtract. Sometimes problems are even more complicated than that, like the expression you have in part 2. If you remove the brackets "[,]" and parentheses "(,)" you see that there are many ways you might calculate the resulting expression. The brackets and parentheses are used to group parts of the expression together.

The procedure is to look at the expression in the most "inside" brackets or parentheses. (This is the B in BEDMAS, B for bracket.) In your example this is

6+1-3x2 perform the multiplication first and then the addition and subtraction. 6 + 1 - 3 x 2 = 6 + 1 - 6 = 1 Hence the problem becomes 5 + 5 - 4 + [6 x 3 - 1 - 5 + 9] Now the expression most "inside" brackets is 6 x 3 - 1 - 5 + 9 = 18 - 1 - 5 + 9 = 21 Finally this gives 5 + 5 - 4 + 21 = 27

The term BEDMAS is just a memory devise to help us remember the order.

Penny


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