4students were scheduled to give book reports in one hour. after the 1st report, 2/3 hour remained. the next two reports too 1/6 hour and 1/4 hour. what fraction of the hour remained?

After the first, we have 2/3 left, the second and third took 1/6 and 1/4, or 5/12 (1/6+1/4=2/12+3/12=(2+3)/12=5/12). Now, we just subtract 5/12 from 2/3, so 2/3-5/12=8/12-5/12=(8-5)/12=3/12=1/4. This means we have 1/4 of an hour left.