###Human: In a block of flats, there are 120 apartments. 85% of them have at least 1 resident, while 60% of the apartments have at least two residents. How many apartments have only one resident?, ### Assistant: At least one person lives in 85/100 * 120 = 102 apartments.
At least two persons live in 60/100 * 120 = 72 apartments.
So in every of the 102 - 72 = 30 apartments, only one person is living. 
 So the answer is :  30