Answer:
(a) $100
(b) $120
Step-by-step explanation:
Part (a):
[tex]$125-(.2*125)[/tex] | Original price minus .2 of the original price, or 20% of the price.
[tex]125-(25)\\100[/tex]
Mary paid $100 for the dress.
Part (b):
Now she wants to sell the dress for a profit of 20%. To set this up, take the price she paid for the dress ($100) and add twenty percent of that price to the 100 dollars. In other words,
[tex]100+(.2*100)\\100+(20)\\120[/tex]
Mary's selling price is $120.