Singapore Math
posted by Ashli .
Lily and Sara each had an equal amount of money at first. After Lily spent $18 and Sara spent $25, Lily had twice as much as Sara. How much money did each of them have at first?

Let the amount each had initially be x.
x  18 = 2*(x  25) = 2x  50
x = 32 
Here is your bar model:
This is a unit bar: [xxx]
Before  the had equal amounts, then they each spent some money. In the end, Lily has twice as much as Sara, or 2 units.
Lily [xxx][xxx]<$18>
Sara [xxx]<$25>
If they started out the same, the second unit bar for Lily must be equal to $25  $18, so $7
[xxx]=$7
Lily had 2 units (2 x $7)+$18 at first.
Sara had 1 unit ($7)+$25 at first.