The apartment has an area of 48 m2, the area of one room is 12 m2, and the other is 21 m2.

The apartment has an area of 48 m2, the area of one room is 12 m2, and the other is 21 m2. What part is the area of other premises from the area of the apartment?

The area of the S (living) rooms is 21 + 12 = 33m².
The area of other premises is S (other) = S (total) – S (residential), where S (total) – total area of the apartment = 48m².
S (others) = 48 – 33 = 15m².
The share of the area of other premises will be S (other) / S (total) = 15/48 = 5/16 = 0.3125 = 31.25%.
Answer: The area of other premises of the apartment is 5/16, or 31.25% of the area of the apartment.