Question

A student's rectangular desk is 30in long and 18in wide. The teacher's desk is similar to the student's desk and has a length of 50in. What is the width of the teacher's desk?

Answer 1

Similar means that the student's desk and the teacher's desk is proportional. 
$\frac{length of teacher's desk}{width of teacher's desk} = \frac{length of student's desk}{width of student's desk}$
$\frac{50}{x} = \frac{30}{18}$
Simplify: $\frac{50}{x} = \frac{5}{3}$
Solve for x. 
50*3=5*x
x=30. in.