Why must we multiply or divide before adding and subtracting?

Question

Can someone explain it in and example? Instead of the doing anything we like answer.. i don't think that's reasonable. Like SI units are used to prevent confusion but the other units still can be used. so there must be a cause.

Answer 1

Well, there is no inherent reason. The reason is a man made construct. We have arbitrarily decided to take it in that order as a part of our "order of operations". If we violated that order, we must group. Groupings themselves are included in the order of operations. If we ignored all those rules, a mathematical expression could have any meaning depending on how we chose to interpret it

Answer 2

let's use something material for our numbers. Question? What is it that we count more than any thing? Of course it is money no matter where your from.
Which result would you prefer???

(10+5*5-4)/2

straight through---
(throw out the parenthesis)
they don't matter either do they?!

10+5*5-4/2=???
10+5=15
15*5=75
75-4=71
71 / 2=$35.50

mathmatically correct
(10+(5*5)-4)/2
(10+25-4)/2
(35-4)/2
31 /2=$16.50
you and a partner did some work. your first job you made $10 then you did 5 jobs for $5 each, you spent $4 on drink and snack then divided the profit with your partner.

WHY WOULD YOU PAY YOUR PARNER MORE THAN THE AMOUNT OF MONEY THAT YOU TOOK IN?

See the progression of the mathmatic "LAWS" do work and the parenthesis do in fact matter also.

Answer 3

Ex: 1 + 4 x 3

First, without multiplying before adding

1 + 4 x 3
= 5 x 3
= 15

Second, with multiplying first

1 + 4 x 3
= 1 + 12
= 13

Basically, it just gives a whole different result. Now normally, we wouldn't need to multiply or divide before adding and subtracting but mathematicians wanted a simple and ordered method of doing things. So.... they made bedmas.

Answer 4

There is a given priority of order in which operations are preformed.
#1)clear parentheses
#2)multiplication
#3)division
#4)addition
#5)subtraction

Answer 5

Just because.

That's how math evolved. In another universe, who knows, maybe the first operation you do is addition. It was simply chosen one way so all people could agree on one answer. Before the Order of Operations, there were many arguments on what answer was the correct answer to all math problems.

Answer 6

3 * 2 + 1 = 7 if we multiply before add
but if we add first you effectively do 3*(2+1)= 9
if you don't follow a convention you don't get consistent results.
The language of math is is that you do multiply and divide first unless you have brackets to explicitly direct otherwise.

Answer 7

It's the order of operations we use.
Have you ever heard of PEMDAS?
It stands for Parentheses, Exponent, Multiplication, Division, Addition, Subtraction.
An easy way to remember it is Please Excuse My Dear Aunt Sally.
This is just a simple way to remember the order of operations.
EX. solve the parentheses before using the exponent because P comes before E in the order of operations.

(2+2)^2
solve 2+2=4
then you square the 4 after you solve what's in the parentheses.


=]

Answer 8

I always thought it was just so everybody can do things in a standard way so we should all get the same answer to the same arithmetic problem. Saves us a bunch of confusion.

Answer 9

That's just the convention for solving problems.
If you want to add or subtract two numbers first you have to put them in parantheses.
That's just so people don't get confused.

Answer 10

Because it avoids ambiguity. Later on it became a generally accepted practice and now is the rule and is being taught as such in schools.