Two dozens of pencils are equal to 2 x 12 = <<2*12=24>>24 pencils.

So the total cost of pencils is $0.5 x 24 = $<<0.5*24=12>>12.

The total cost of folders is $0.9 x 20 = $<<0.9*20=18>>18.

Thus, the cost to buy the office supplies is $12 + $18 = $<<12+18=30>>30.

# Answer

30
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
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?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
30
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?
train