fleet automation approximately 66% ( 66 % ) of our residential routes have been converted to automated single driver trucks . by converting our residential routes to automated service , we reduce labor costs , improve driver productivity and create a safer work environment for our employees . additionally , communities using automated vehicles have higher participation rates in recycling programs , thereby complementing our initiative to expand our recycling capabilities . fleet conversion to compressed natural gas ( cng ) approximately 12% ( 12 % ) of our fleet operates on natural gas . we expect to continue our gradual fleet conversion to cng , our preferred alternative fuel technology , as part of our ordinary annual fleet replacement process . we believe a gradual fleet conversion is most prudent to realize the full value of our previous fleet investments . approximately 50% ( 50 % ) of our replacement vehicle purchases during 2013 were cng vehicles . we believe using cng vehicles provides us a competitive advantage in communities with strict clean emission objectives or initiatives that focus on protecting the environment . although upfront costs are higher , we expect that using natural gas will reduce our overall fleet operating costs through lower fuel expenses . standardized maintenance based on an industry trade publication , we operate the eighth largest vocational fleet in the united states . as of december 31 , 2013 , our average fleet age in years , by line of business , was as follows : approximate number of vehicles average age .

approximate number of vehicles: residential: 7600
commercial: 4300
industrial: 3600
total: 15500
average age: residential: 7
commercial: 6
industrial: 9
total: 7

through standardization of core functions , we believe we can minimize variability in our maintenance processes resulting in higher vehicle quality while extending the service life of our fleet . we believe operating a more reliable , safer and efficient fleet will lower our operating costs . we have completed implementation of standardized maintenance programs for approximately 45% ( 45 % ) of our fleet maintenance operations as of december 31 , 2013 . cash utilization strategy key components of our cash utilization strategy include increasing free cash flow and improving our return on invested capital . our definition of free cash flow , which is not a measure determined in accordance with united states generally accepted accounting principles ( u.s . gaap ) , is cash provided by operating activities less purchases of property and equipment , plus proceeds from sales of property and equipment as presented in our consolidated statements of cash flows . for a discussion and reconciliation of free cash flow , you should read the 201cfree cash flow 201d section of our management 2019s discussion and analysis of financial condition and results of operations contained in item 7 of this form 10-k . we believe free cash flow drives shareholder value and provides useful information regarding the recurring cash provided by our operations . free cash flow also demonstrates our ability to execute our cash utilization strategy , which includes investments in acquisitions and returning a majority of free cash flow to our shareholders through dividends and share repurchases . we are committed to an efficient capital structure and maintaining our investment grade rating . we manage our free cash flow by ensuring that capital expenditures and operating asset levels are appropriate in light of our existing business and growth opportunities , as well as by closely managing our working capital , which consists primarily of accounts receivable , accounts payable , and accrued landfill and environmental costs. .

Questions:
as of december 31, 2013, what was the number of residential vehicles?
and what was the number of industrial ones?
how much, then, does the residential fleet number represent in relation to this industrial one?
and as of that same date, what was the amount of vehicles operating on compressed natural gas ( cng )?

Answers:
7600
3600
2.11
1860