A survey of 70 college students showed the following data: 42 had a car; 50...

Step 1 
According to a survey of 70 college students, 42 had a car, 50 had a TV, 30 had a bicycle, 17 owned both a car and a bicycle, 35 owned both a car and a television, 
Step 2 
That is, ${\displaystyle n\left(C\right)=43,n\left(T\right)=50,n\left(B\right)=30,n\left(C\text{and}B\right)=17,n\left(C\text{and}T\right)=35,n\left(T\text{and}B\right)=25\text{and}n\left(C\text{and}T\text{and}B\right)=15}$. 
Total students is ${\displaystyle n=70}$. 
Thus, the number of students, who had either car or TV or bicycle is, 
${\displaystyle n\left(C\text{or}T\text{or}B\right)=n\left(C\right)+n\left(T\right)+n\left(B\right)-n\left(C\text{and}B\right)-n\left(C\text{and}T\right)-n\left(T\text{and}B\right)+n\left(C\text{and}T\text{and}B\right)=43+50+30-17-35-25+15=61}$. 
Thus, the number of students, had none of the three items is ${\displaystyle n-n\left(C\text{or}R\text{or}B\right)=70-61=9}$.