Achoir teacher is dividing 3 sopranos and 12 altos into singing groups. he wants each group to have the same combination of sopranos and altos, with no singers left over. what is the greatest number of groups he can make?

Awoman has 14 different shirts: 10 white shirts and 4 red shirts. if she randomly chooses 2 shirts to take with her on vacation, then what is the probability that she will choose two white shirts? show your answer in fraction and percent, round to the nearest whole percent.