An orange costs $.09. How much would 2 dozen oranges cost?

Another way of thinking about it that may help you do things like this in your head. If you wished to do so.
##$2.16##
##color(brown)(“There is no reason why you should not write down a few numbers”)## ##color(brown)(“but still do a lot of the working out in your head.”)##
Doing it is much quicker than explaining it
‘~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The calculation we need to do is ##24xx$0.09##
Let’s explore another way of doing it…..
1 dozen is 12, so 2 dozen is ##2xx12##
But ##12 = 10+2##
Multiplying a number by 10 or 2 is much easier than multiplying by 12.
‘~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
##10xx$0.09 = $0.90##
##color(white)(1)2xx$0.09=ul($0.18)” “larr” add”##
##” “$1.08##
‘~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
So ##12xx$0.09=$1.08##
So ##24xx$0.09=2xx09=2xx$1.08= $2.16##