I think you need to subtract 250-20=230. So Margo payed $230 for the computer. Hope this helps.
The answer is $1000.
Firstly, we know that $250 is 20% of the original cost. Because of this we multiply $250 by 5, to get 100%=$1250.
Because she saved $250, we take this away from $1250, to get a final answer of $1000.
