Math story problem

Question

An apartment building contains 12 units consisting of one and two bedroom apartments that rent for $360 and $450 per month, respectively. When all units are rented, the total monthly rental is $4,950. What is the number of two-bedroom apartments?

Answer 1

Let x = the number of one bedroom apartments

Let y = the number of two bedroom apartments

x + y = 12      x = 12 - y

360x + 450y = 4950

360(12 - y) + 450y = 4950

4320 - 360y + 450y = 4950

90y = 630

y = 7