A school knows that 38% of its incoming students own a smart phone and a tablet. what percent of students who own a smartphone also own a tablet if 84% of students own a smart phone

We know that

38% of the incoming students own both a smartphone and a tablet

84% of the students own a smartphone

We are asked to find the percentage of students who own a smartphone

Let N be the total number of incoming students and S be the total number of students

So,

(N (38%) + S (84%)) / (N + S)

If we know the total number of students or incoming students, we can solve for the percentage by substituting the value of N or S