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?
Two dozens of pencils are equal to 2 x 12 = 
<gadget id="calculator">2*12</gadget>
<output>24</output>
24 pencils.
So the total cost of pencils is $0.5 x 24 = $
<gadget id="calculator">0.5*24</gadget>
<output>12</output>
12.
The total cost of folders is $0.9 x 20 = $
<gadget id="calculator">0.9*20</gadget>
<output>18</output>
18.
Thus, the cost to buy the office supplies is $12 + $18 = $
<gadget id="calculator">12+18</gadget>
<output>30</output>
30.

<result>30</result>