What is $12+ [ - 4+ ( - 9) ]$ ?

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Answer 1 · 2016-09-20T10:26:06

$-1$

Count the number of terms first. Each term simplifies to a single answer and these are added or subtracted in the last line.

$color(blue)(12)+[-4color(red)(+(-9))]" "larr$ start with the inner-most brackets.

= $color(blue)(12)+[-4color(red)(-9)]$

= $color(blue)(12)+[color(red)(-13)]$

= $color(blue)(12)color(red)(-13)$

= $-1$

Terms which are already simplified should be carried down to the next line.

What is 12+ [ - 4+ ( - 9) ]12+ [ - 4+ ( - 9) ]?