table of contents ( 4 ) the increase in cash flows was primarily due to the timing of inventory purchases and longer payment terms with certain vendors . in order to manage our working capital and operating cash needs , we monitor our cash conversion cycle , defined as days of sales outstanding in accounts receivable plus days of supply in inventory minus days of purchases outstanding in accounts payable , based on a rolling three-month average . components of our cash conversion cycle are as follows: .

Table: ( in days ) december 31 , 2017 december 31 , 2016 december 31 , 2015 days of sales outstanding ( dso ) ( 1 ) 52 51 48 days of supply in inventory ( dio ) ( 2 ) 12 12 13 days of purchases outstanding ( dpo ) ( 3 ) -45 ( 45 ) -44 ( 44 ) -40 ( 40 ) cash conversion cycle 19 19 21

( 1 ) represents the rolling three-month average of the balance of accounts receivable , net at the end of the period , divided by average daily net sales for the same three-month period . also incorporates components of other miscellaneous receivables . ( 2 ) represents the rolling three-month average of the balance of merchandise inventory at the end of the period divided by average daily cost of sales for the same three-month period . ( 3 ) represents the rolling three-month average of the combined balance of accounts payable-trade , excluding cash overdrafts , and accounts payable-inventory financing at the end of the period divided by average daily cost of sales for the same three-month period . the cash conversion cycle was 19 days at december 31 , 2017 and 2016 . the increase in dso was primarily driven by higher net sales and related accounts receivable for third-party services such as saas , software assurance and warranties . these services have an unfavorable impact on dso as the receivable is recognized on the consolidated balance sheet on a gross basis while the corresponding sales amount in the consolidated statement of operations is recorded on a net basis . this also results in a favorable impact on dpo as the payable is recognized on the consolidated balance sheet without a corresponding cost of sales in the statement of operations because the cost paid to the vendor or third-party service provider is recorded as a reduction to net sales . in addition , dpo also increased due to the mix of payables with certain vendors that have longer payment terms . the cash conversion cycle was 19 and 21 days at december 31 , 2016 and 2015 , respectively . the increase in dso was primarily driven by higher net sales and related accounts receivable for third-party services such as saas , software assurance and warranties . these services have an unfavorable impact on dso as the receivable is recognized on the balance sheet on a gross basis while the corresponding sales amount in the statement of operations is recorded on a net basis . these services have a favorable impact on dpo as the payable is recognized on the balance sheet without a corresponding cost of sale in the statement of operations because the cost paid to the vendor or third-party service provider is recorded as a reduction to net sales . in addition to the impact of these services on dpo , dpo also increased due to the mix of payables with certain vendors that have longer payment terms . investing activities net cash used in investing activities increased $ 15 million in 2017 compared to 2016 . capital expenditures increased $ 17 million to $ 81 million from $ 64 million for 2017 and 2016 , respectively , primarily related to improvements to our information technology systems . net cash used in investing activities decreased $ 289 million in 2016 compared to 2015 . the decrease in cash used was primarily due to the completion of the acquisition of cdw uk in 2015 . additionally , capital expenditures decreased $ 26 million to $ 64 million from $ 90 million for 2016 and 2015 , respectively , primarily due to spending for our new office location in 2015 . financing activities net cash used in financing activities increased $ 514 million in 2017 compared to 2016 . the increase was primarily driven by changes in accounts payable-inventory financing , which resulted in an increase in cash used for financing activities of $ 228 million and by share repurchases during 2017 , which resulted in an increase in cash used for financing activities of $ 167 million . for more information on our share repurchase program , see part ii , item 5 , 201cmarket for registrant 2019s common equity , related stockholder matters and issuer purchases of equity securities . 201d the increase in cash used for accounts payable-inventory financing was primarily driven by the termination of one of our inventory financing agreements in the fourth quarter of 2016 , with amounts .

Question: by what percentage did the cash conversion cycle decrease from dec 31 , 2015 to dec 31 , 2016?
Answer: 9.5%
Calculation: multiply(divide(subtract(21, 19), 21), const_100)