Trade payables payment period

Which of the following is likely to reduce the trade payables payment period? A Paying trade suppliers within seven days of reciept of invoice to obtain a discount B Buying an increasing volume of credit purchases during an accounting period Sir the correct answer was A I was wondering why isn't B the answer because in the formula for trade payable period it is. (trade payables/credit purchases )*365 so if credit purchases changes then trade payable period also could change right???