What is #[7+(10-:5-9)]-9#?

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Answer 1 · 2018-03-04T04:05:07

#-9#

We can use PEMDAS:

#color(red)(P)# - Parentheses (also known as Brackets)
#color(blue)(E)# - Exponents
#color(green)(M)# - Multiplication
#color(green)(D)# - Division (this has the same weight as M and so I gave it the same colour)
#color(brown)(A)# - Addition
#color(brown)(S)# - Subtraction - (again, same weight as A and so the same colour)

#[7+(10-:5-9)]-9#

We first look for #color(red)(P)#:

#color(red)([7+(10-:5-9)]#

Inside this bracket is another one:

#color(red)(10-:5-9)#

We have two operations here - division and subtraction. See that #color(green)(D)# comes before #color(brown)(S)#:

#color(green)(10-:5)color(brown)(-9)#

#color(green)2color(brown)(-9)#

#color(brown)(-7)#

Since we now know that #(10-:5-9)=-7#, we can substitute that back into the original:

#[7+(10-:5-9)]-9=[7+(-7)]-9#

What we have left is addition and subtraction, and so we work from left to right:

#[7+(-7)]-9=[0]-9=-9#