human
A pencil costs $0.5 each and a folder costs $0.9 each. An office needs two dozen pencils and 20 pieces of folders. How much does it cost to buy the office supplies?
assistant
How many pencils are in two dozen? ** Two dozens of pencils are equal to 2 x 12 = <<2*12=24>>24 pencils.
How much do the pencils cost? ** So the total cost of pencils is $0.5 x 24 = $<<0.5*24=12>>12.
How much do the folders cost? ** The total cost of folders is $0.9 x 20 = $<<0.9*20=18>>18.
How much does it cost to buy the office supplies? ** Thus, the cost to buy the office supplies is $12 + $18 = $<<12+18=30>>30.
#### 30