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?
Let's be accurate as possible and think first.
30
Two dozens of pencils are equal to 2 x 12 = 24 pencils.

So the total cost of pencils is $0.

5 x 24 = $12.

The total cost of folders is $0.

9 x 20 = $18.

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

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Final answer: 30