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? Let's be accurate as possible.
First find the total number of records that can fit on all the shelves: 4 cases * 3 shelves / case * 20 records / shelf = 240 records. Then multiply that number by 60% to find the number of records actually on the shelves: 240 records * 60% = 144 records. Then multiply that number by 60 to find the number of ridges on all the records: 144 records * 60 ridges / record = 8640 ridges.
The answer: 8640.