There are 60 ridges on a vinyl record. Jerry has 4 cases, each with 3 shelves that can hold 20 records each. If his shelves are 60% full, how many ridges are there on all his records?
First find the total number of records that can fit on all the shelves: 4 cases * 3 shelves/case * 20 records/shelf = 
<gadget id="calculator">4*3*20</gadget>
<output>240</output>
240 records.
Then multiply that number by 60% to find the number of records actually on the shelves: 240 records * 60% = 
<gadget id="calculator">240*60*.01</gadget>
<output>144</output>
144 records.
Then multiply that number by 60 to find the number of ridges on all the records: 144 records * 60 ridges/record = 
<gadget id="calculator">144*60</gadget>
<output>8_640</output>
8640 ridges.

<result>8_640</result>