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: subtract(21, 19), divide(#0, 21), multiply(#1, const_100)