why no a*b+c

Duplicate
$a + ($b + $c) = $a + ($b + $c)
$a*$b+$c =($a*$b)+$c

... basic math

this ($a * $b) * $c is the same like this $a * $b * $c
($a + $b) + $c = $a + ($b + $c)
and ...
duplicate !!!
this is basic knowladge in math