a building has a total of 60 one-bedroom and two-bedroom apartments. there are twice as many one-bedroom apartments as two-bedroom apartments. how many apartments of each type are in the building? Use a system of linear equations to justify your answer.

Let the number of one-bedroom apartments be x, and the number of two-bedroom apartments be y.
If there are a total of 60, then x + y = 60.
If there are twice as many 1-bedroom apartments as there are 2-bedroom ones, then x = 2y.
Substitute x = 2y into the first equation to get 2y + y = 60, or y = 20.
Substitute y = 20 into the second equation to get x = 40.
Therefore, there are 40 one-bedroom apartments and 20 two-bedroom apartments in the building.