66. In the box, there are 100 balls of different colors: 28 red balls, 20 green balls, 12 yellow balls, 20 blue balls, 10 white balls, and 10 black balls. If you randomly draw balls from the box, how many balls must you draw to ensure that you have 15 balls of the same color? $\qquad$
Answer: 75.
Solution: Considering the worst-case scenario, all 12 yellow balls, 10 white balls, and 10 black balls are taken out, along with 14 red balls, 14 green balls, and 14 blue balls, totaling 12+10+10+14+14+14=74 balls, none of which contain 15 balls of the same color. As long as one more ball is taken, this ball can only be one of red, green, or blue, and thus 15 balls of the same color will appear.

Therefore, at least 75 balls must be taken out to ensure that there are 15 balls of the same color.