Hello.
The solutions found to radical equations are not necessarily viable. They sometimes result in inequalities, and have to be checked.
Hope I helped.
        
                    
             
        
        
        
The percent of discount is 70%.
        
             
        
        
        
Here is a method that makes it seem easier. 
<span>Write down any number between 51 and 59. </span>
<span>For example you might choose 57 = 3*19 </span>
<span>Divide both numbers by 10 and write the answer as </span>
<span>0.3 * 1.9 = 0.57</span>