If 2 men or 6 women or 4 boys can finish a work in 99 days, how many days will one man, one woman, and one boy together take to finish the same work?

1 man's 1 day's work = 1/(99 × 2)
= 1/198;
1 women's 1 day's work = 1/(99 × 6)
= 1/594;
1 boy's 1 day's work = 1/(99 × 4)
= 1/396.
(1 man + 1 woman + 1 boy's)'s 1 day's work
{(1/198) + (1/594) + (1/396)}
= 11/1188
= 1/108.
Hence, 1 man, 1 woman and 1 boy together take 108 days to finish the same work.