Explanation:
Kyle can do in 1 minute 1/30 of the work.
Michael can do in 1 minute 1/40 of the work.
the whole work is 1.
how much can they do together in 16 minutes ?
16×1/30 + 16×1/40 = 8/15 + 2/5 = 8/15 + 3/3 × 2/5 =
= 8/15 + 6/15 = 14/15
which is less than 1 = 15/15.
so, as they cannot even do the whole work in 16 minutes, they cannot do it in less than 16 minutes either.