She is incorrect as 10% of the higher marked up price is larger than 10% of the original price.
For example: If you mark up $100 by 10% you get $110.
If you mark down $110 by 10%, you will get $99, as 10% of $110 ($11) is larger than 10% of $100 ($10).
        
             
        
        
        
Answer:
B
Step-by-step explanation:
So we have the expression: 

Since 5 goes into both 15 and 50, we can factor out a 5. First, rewrite the numbers as: 

Factor out the 5: 

So, our answer is B
And we're done!
 
        
             
        
        
        
Answer:
The first and third is correct.
Step-by-step explanation:
I'm not a expert but I know its right.