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Jsmitheh
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26 May 2009, 8:34 am

I found an old maths book the other day and decided to look at it. For some reason these incredibly easy questions make no sense to me.

21 + 32 / (-4) + (-6)

I simplified it as

53 / -10
-5.3

But apparently it's 7, how is this?


[366 / (-6) - (-6)] / (-11)
I simplified it as
[366 / 0] / - 11

how can you divide by zero?

Apparently the answer is 5.



Aleph0
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26 May 2009, 8:46 am

Jsmitheh wrote:
I found an old maths book the other day and decided to look at it. For some reason these incredibly easy questions make no sense to me.

21 + 32 / (-4) + (-6)

I simplified it as

53 / -10
-5.3

But apparently it's 7, how is this?


[366 / (-6) - (-6)] / (-11)
I simplified it as
[366 / 0] / - 11

how can you divide by zero?

Apparently the answer is 5.


Okay,
21 + 32 / (-4) + (-6) = 21 -(32/4) -6 = 21 -8 -6 = 21 -14 = 7;

[366 / (-6) - (-6)]/ (-11) = [(366/-6) +6]/-11) = [-(366/6) +6]/(-11) =
[-61+6]/(-11) = (-55)/(-11) = 55/11 = 5;

Hope this helps!



b9
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26 May 2009, 9:03 am

Jsmitheh wrote:
I found an old maths book the other day and decided to look at it. For some reason these incredibly easy questions make no sense to me.

21 + 32 / (-4) + (-6)

I simplified it as

53 / -10
-5.3

But apparently it's 7, how is this?


i have not much time to describe for now, but it is an example of the priority of process of of the operands.
i see it as this:

21 + (32 / (-4) + (-6))

now 32/-4 = -8

so 21-8 is 13.
and if you add -6 to 13 you get 7.



ruveyn
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26 May 2009, 11:38 am

Jsmitheh wrote:
I found an old maths book the other day and decided to look at it. For some reason these incredibly easy questions make no sense to me.

21 + 32 / (-4) + (-6)

I simplified it as

53 / -10
-5.3

But apparently it's 7, how is this?



You grouped the terms incorrectly. This should be read as:

21 + (32/-4) + (-6)

which comes out to 21 - 8 - 6 = 7

In general / and * are done before + and - in a complex expression.

If there is any doubt, parentheses should be used.

For example what is 8/2*4? It is either 8/2 * 4 ( = 16) or 8/(2*4) ( = 1 ). The parens should be used to resolve ambiguity.

ruveyn



Fayed
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26 May 2009, 1:17 pm

Order or Operations

PEDMAS (ped-ma-s)

or

Please Excuse My Dear Aunt Sally

Parenthesis, Exponents, Division or Multiplication, Addition or Subtraction.

Goes from left to right.