increase in dividends paid .free cash flow is defined as cash provided by operating activities less cash used in investing activities and dividends paid .free cash flow is not considered a financial measure under accounting principles generally accepted in the u.s .( gaap ) by sec regulation g and item 10 of sec regulation s-k and may not be defined and calculated by other companies in the same manner .we believe free cash flow is important to management and investors in evaluating our financial performance and measures our ability to generate cash without additional external financings .free cash flow should be considered in addition to , rather than as a substitute for , cash provided by operating activities .the following table reconciles cash provided by operating activities ( gaap measure ) to free cash flow ( non-gaap measure ) : millions 2013 2012 2011 .
[['millions', '2013', '2012', '2011'], ['cash provided by operating activities', '$ 6823', '$ 6161', '$ 5873'], ['cash used in investing activities', '-3405 ( 3405 )', '-3633 ( 3633 )', '-3119 ( 3119 )'], ['dividends paid', '-1333 ( 1333 )', '-1146 ( 1146 )', '-837 ( 837 )'], ['free cash flow', '$ 2085', '$ 1382', '$ 1917']]
2014 outlook f0b7 safety 2013 operating a safe railroad benefits our employees , our customers , our shareholders , and the communities we serve .we will continue using a multi-faceted approach to safety , utilizing technology , risk assessment , quality control , training and employee engagement , and targeted capital investments .we will continue using and expanding the deployment of total safety culture and courage to care throughout our operations , which allows us to identify and implement best practices for employee and operational safety .derailment prevention and the reduction of grade crossing incidents are also critical aspects of our safety programs .we will continue our efforts to increase detection of rail defects ; improve or close crossings ; and educate the public and law enforcement agencies about crossing safety through a combination of our own programs ( including risk assessment strategies ) , various industry programs and local community activities across our network .f0b7 network operations 2013 we believe the railroad is capable of handling growing volumes while providing high levels of customer service .our track structure is in excellent condition , and certain sections of our network have surplus line and terminal capacity .we are in a solid resource position , with sufficient supplies of locomotives , freight cars and crews to support growth .f0b7 fuel prices 2013 uncertainty about the economy makes projections of fuel prices difficult .we again could see volatile fuel prices during the year , as they are sensitive to global and u.s .domestic demand , refining capacity , geopolitical events , weather conditions and other factors .to reduce the impact of fuel price on earnings , we will continue seeking cost recovery from our customers through our fuel surcharge programs and expanding our fuel conservation efforts .f0b7 capital plan 2013 in 2014 , we plan to make total capital investments of approximately $ 3.9 billion , including expenditures for positive train control ( ptc ) , which may be revised if business conditions warrant or if new laws or regulations affect our ability to generate sufficient returns on these investments .( see further discussion in this item 7 under liquidity and capital resources 2013 capital plan. ) f0b7 positive train control 2013 in response to a legislative mandate to implement ptc by the end of 2015 , we have invested $ 1.2 billion in capital expenditures and plan to spend an additional $ 450 million during 2014 on developing and deploying ptc .we currently estimate that ptc , in accordance with implementing rules issued by the federal rail administration ( fra ) , will cost us approximately $ 2 billion by the end of the project .this includes costs for installing the new system along our tracks , upgrading locomotives to work with the new system , and adding digital data communication equipment to integrate the various components of the system and achieve interoperability for the industry .although it is unlikely that the rail industry will meet the current mandatory 2015 deadline ( as the fra indicated in its 2012 report to congress ) , we are making a good faith effort to do so and we are working closely with regulators as we implement this new technology. .

Question: what percentage of cash provided by operating activities were dividends paid in 2013?
Answer: 20%