Most of "at least" probability questions have to be reversed.
You can calculate the number of possibilities in which there are 1, 2 or 3 french speakers in the group.
But it is most simple to calculate 1) the total number of possibilities and 2) the possibilities in which there is 0 french.
Total possibilities= Possibilities with at least one french + possibilities with 0 french
Total possibilities, we have 10 members in total and we choose only 3.
Total possibilities: 10C3=120
We do not want any french speaker, so we choose 3 members among 6.
Possibilities of a 3-members group with 0 french speakers: 6C3=20
120-20=100
GmatPrep #5
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Source: Beat The GMAT — Problem Solving |
