There are red and white balls in a pile of balls, 48 red balls out of 50 balls taken out for the first time, 6 red balls out of 7 balls taken out each time, so that 90% of the balls taken out are red balls , then how many times to take to meet the requirements.
一堆球中有红白两种球，第一次取出的50个球中有48个红球，以后每次取出7个球中6个红球，要使取出的球中红球占90%，那么要取多少次才能满足要求．
<result>11</result>