Given 
A survey found that 12 out of 30 people preferred bacon over sausage. 
Find out the what percent of people prefer bacon over sausage.
To proof 
As given in the question
survey found that 12 out of 30 people preferred bacon over sausage.
Total number of people = 30
people preferred bacon over sausage = 12
Formula 
 
 
 
put the value in the formula

solve the above 
 percent of people prefer bacon over sausage = 40 %
Hence proved