21 is 42% of 50. To do that, you divide 21 by 50, you get .42. You then multiply .42 by 100 to get your answer. 
        
                    
             
        
        
        
Answer:
Step-by-step explanation:
a )
 probability of a computer being ancient = .99
probability of a computer being cutting-edge =.01 
probability of two selected  computer being old 
= .99 x .99 
= .98 or 98%
b ) 
probability of 5 selected computers being old 
= .99 x .99 x .99 x .99 x .99
= .95 or 95%
c )
probability that at least one of the five selected computers is cutting-edge 
= 1 - probability of 5 selected computers being old 
= 1 - .95 
= .05 
5 %
 
        
             
        
        
        
IS this from a book or online
        
             
        
        
        
It is called the payback period
        
             
        
        
        
He can make 2 batches of cookies. I'm not sure about the leftover cups because you wrote sugar twice