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Order of operations
By Anonymous on Wednesday, May 16, 2001 - 05:19 pm:

A teacher at our school insists that
3=10 - 2 + 5 is correct
as is
3 = 10 - (2 + 5) correct.
We have told her that the first one is incorrect as the answer book says, but she insists that the laws of algebra state that addition is done first - brackets or no brackets.
Please clarify

By Mike Pearson (Gmp26) on Wednesday, May 16, 2001 - 05:33 pm:

You are right - the first is incorrect, and the second is correct.

Multiplication must be done before addition if there are no brackets indicating the contrary.

In this case the order does not matter since
10 - 2 + 5 = 10 + (-2 + 5) = (10 - 2) + 5

none of which equal 10 - (2+5)

Mike

By The Editor:

This confusion often arises because of the mnemonic BODMAS or BIDMAS.

The letters stand for the different operations as shown below, but it is important to remember that D and M are joint third, and A and S are joint fifth, so addition does not come before subtraction.

B Brackets ()

O Order/Of/Operation or I Indices

D Division ÷
M Multiplication ×

A Addition +
S Subtraction -