Re: [Math4u] Re: 26 - 14 : 2 x 3 + 4² = ?

Precedence and priorities are two different things.

 

(1) Addition and Subtraction have the same priority as they are the same order of operations.

(2) Mixed operations can always be solved from left to right among the same order of operations.

(3) However, when we choose a random order, subtraction has precedence over addition, and not the other way around. This fact simplifies calculations as well where it can be applied.

(4) Similar consideration applies to multiplication and division.

 

Vinaire

----- Original Message ----
From: Rob van Wijk <robvanwijk@gmx.net>
To: Math4u@yahoogroups.com
Sent: Tuesday, November 27, 2007 6:26:56 AM
Subject: Re: [Math4u] Re: 26 - 14 : 2 x 3 + 4² = ?

Vinaire <vinaire@yahoo. com> wrote:
> (..)
> For example, 84 + 97 - 87 is much easier to execute with subtraction
> first, compared to left to right rule.
> Similarly, 42 x 46 / 23 is much easier to execute with division first.
>
> Vinaire
>

Uhm yeah, and 54 + 46 - 37 is easier with addition first. Nice examples,
but they've been specifically constructed to work out nicely (97-87 = 10,
a round number, 46/23 = 2, also a round number). I agree "substraction
first" will keep numbers smaller and might therefore be somewhat easier
in practice (unless working with negative numbers...), but the question
was about the precedence of operators, not tricks to make mental math a
little easier. (Note that I called the trick "pointless" (which might've
been an overly harsh conclusion), I *didn't* call it "wrong".)

Grtz,
Rob

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