27 replies to this topic

[Golan]

ultra1437, on 10 May 2011, 22:05, said:

the first 2 in the equation was the coefficient of the sum in the parenthesis (brackets) [ 2(1+2) ] is really two steps in one, you do what's inside the brackets, then multiply the sum by the coefficient, THEN you can divide 6 by it.

Uh, no you don't. You divide by the expression succeeding the division sign which in this case is 2. The bracket is a different expression on which the implicit multiplication works. If you want the division to work with the entire expression of 2(1+2), you have to express this by grouping the two expressions into a single expression using brackets around it, i.e. (2(1+2)).

[R3ven]

Using PEMDAS(parenthesis, exponents, multiplication, division, add, subtract):

6/2(1+2)
6/2(3)
6/6
1

[Golan]

A common technique for remembering the order of operations is the abbreviation "PEMDAS", which is turned into the phrase "Please Excuse My Dear Aunt Sally". It stands for "Parentheses, Exponents, Multiplication and Division, and Addition and Subtraction". This tells you the ranks of the operations: Parentheses outrank exponents, which outrank multiplication and division (but multiplication and division are at the same rank), and these two outrank addition and subtraction (which are together on the bottom rank). When you have a bunch of operations of the same rank, you just operate from left to right. For instance, 15 ÷ 3 × 4 is not 15 ÷ 12, but is rather 5 × 4, because, going from left to right, you get to the division first.