vtran
In an apartment building that has 490 units, 4 out of every 7 units are currently rented, including 1/5 of the one-bedroom units. If, of the rented apartments, there is a 6:1 ratio of two-bedroom units to one-bedroom units, and the building only consists of two-bedroom and one-bedroom units, how many two-bedroom units are not rented?
(A) 50
(B) 70
(C) 100
(D) 105
(E) 140
Since 4 out of 7 apartments in the building are rented out, the number of apartments rented out is (4/7)(490) = 280.
We can let the ratio of two-bedroom units to one-bedroom units = 6x : x; thus, the total number of rented apartments is 7x and we can create the following equation:
7x = 280
x = 40
Thus, we have 6(40) = 240 two-bedroom apartments and 40 one-bedroom apartments that are rented out.
Since the 40 one-bedroom apartments that are rented out represent 1/5 of all the one-bedroom apartments in the building, the number of one-bedroom apartments in the building is 40/(1/5) = 200. Thus, there are 490 - 200 = 290 two-bedroom apartments in the building. Finally, since 240 two-bedroom apartments are rented out, 290 - 240 = 50 two-bedroom apartments are not rented out.
Answer: A