Answer:
192 
Step-by-step explanation:
To find how many phones are expected to be defective, we need to represent the values in a fraction.

x = number of defective phones
Now we can solve this using algebra.
To get the value of x we need to multiply both sides by 8000 to leave x alone.



So around 192 cell phones are expected to be defective out of 8000 phones.
 
        
             
        
        
        
Step-by-step explanation:
We use 

Now we have

Hope that useful for you
 
        
             
        
        
        
To find the final term to compete the square you need to divide the 'x' term by 2 then square it

 - equivalent equation