Theres 3 japanese, to have at least one you can have one, two or three. If you have 1 japanese, then 3 will be not japanese, ie 3C1*7C3. Similarly 2 japanese and 2 not japanese: 3C2*7C2 and 3 japanese and 1 not is 3C3*7C1. Add these together and divide by the total outcomes for the probability