We can create an equation to represent this situation.
Let #x# = the total amount of money that Mary had at first (before she bought anything.)
Mary started with #color(blue)(x)# dollars. After she spent #color(red)(2/5)# of her #color(blue)("money")# on a handbag and #color(violet)($20)# on a belt, she had #color(green)($25)# left.
#color(green)(25) = color(blue)(x) - color(red)(2/5) color(blue)(x) - color(violet)(20)#
1. Combine like terms.
#25 = 3/5x - 20#
2. Add 20 to both sides.
#25 + 20 = 3/5x cancel( -20) cancel(+20)#
#45 = 3/5x#
3. Divide both sides by #3/5# (or multiply both sides by #5/3# - shown here) to find x.
#(5/3)45 = 3/5x(5/3)#
#x = 75#
She had $75 at first.
Hope this helps!
