15%
amount error is guess subtract actual amount 198-172 = 26
26/172 = 0.15 
0.15 x100 = 15%
        
                    
             
        
        
        
Answer:
put formula a square minus b square
 
        
             
        
        
        
Answer:
5 apples
Step-by-step explanation:
First, we must find the cost of one apple
12/20 = the cost of one apple
= $0.60
Then, we divide 3 by the price of one apple
3/0.6 = amount of apple we can buy
= 5
 
        
             
        
        
        
Alright so lets start with an arbitrary amount of students. Just to help us visualize the problem.
Say, 100 students for the first year when it was founded?
So far,
1996 - 100 students
From 96' to 97', it doubles. So:
1996 - 100 students
1997 - 200 students
From 97' to 98', it doubles AGAIN.
1996 - 100 students
1997 - 200 students
1998 - 400 students
So, what the percentage increase from 100, to 400? 
Well, 100 x 4 gives us 400, so it's a 400 percent increase.
 
        
                    
             
        
        
        
The answer is 7,500. 
Hope that helped!!!