Equation:
Total = Band Only + Orchestra Only + Both
Band Only + Orchestra Only = 80%
Band Only = 50%
Orchestra Only = 30%
Therefore:
Band = 100% - Orchestra Only 30% = 70%
70% of total students = 119 
Total students = 170 
Number of Students in Orchestra Only: 
= ===> 30% of 170 = 51
 
 
Solution for what is 30% of 170: 
170 / x = 100 / 30 
(170 / x) * x = (100 / 30) * x (we multiply both sides of the equation by x) 
170 = 3.33333333333 * x (we divide both sides of the equation by )(3.33333333333) to get x 
170 / 3.33333333333 = x 
51 = x 
x = 51 
 
now we have:  
30% of 170 = 51 
 
Therefore your, Answer is ========> 51 students is in the Orchestra only.
Hope that helps!!!!! : )