Question

Betty had $40 in her pocket. She bought 12 identical bags of popcorn. Betty was left with $10 after buying the popcorn. What was the price, in dollars, of each bag of popcorn?

Answer 1

One bag cost her $2.50 because if you multiply 2 by 12 equals 24 then you do .50 multiply 12 equals 6 then add 24 and 6 equals $30

Answer 2

Each bag of popcorn costs $2. 5 
You can solve it by creating an equation. This one can be: 
40 -12x = 10
Undo the operation. 
40 -12x = 10
-40 -12x = 10 -40
Eliminate the 40. This will live you with the following.
-12x = -30
Divide -12x by -12. Do the same with the -30
-12x = -30/ -12
This will give you the answer.
x = 2.5