Aschool 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

No. of students own a smart phone=B= 84%
No.of students own a tablet=A
No. of students own a smart phone and tablet= A∩B =38%

We use the conditional probability to do this problem;
                           Pr(A|B)=Pr(A∩B)/Pr(B)
                                       =0.38/0.84
                                       =0.45
                                       =45%(no. of students own a smartphone also own a tablet)

B, 0.4 repeats so it is rational and square root of 16 is 4 so that is rational as well.