I have no idea why I'm even attempting this one:
Say total leaves = 800
Travis = T leaves/hour
Cybil = C leaves/hour
t = time (hours) = 8
t(T+C) = 800
8(T+C) = 800
With (I) T = 1.5C, plugging in you get C = 40 leaves/hour
If C = 40, T = 60 leaves/hour
With (II) T = 2C, plugging in you get C = (100/3) leaves/hour
IF C = 100/3, T = 200/3 leaves/hour
With (II) T = 3C, plugging in you get C = 25 leaves/hour
If C = 25, T = 75 leaves/hour
Now we know that if T works for 20 min and swims for 20 min, so his actual rate of working is double his average. And if we switch everything to 20 min increments
(I) (40/3)n + (n-1)(60*2)/(3) = 800
Solving for n = 15 plus a fraction
So, on the 15 increment, T will be working because n is odd. But since n = 15 and change, T will swimming.
(II) (100/3)n + (n-1)(200*2)/3 = 800
Solving for n = 12 plus a fraction
So, on the 12 increment, T will be swimming because n is even. But since n = 12 and change, T will be working.
(III) (25/3)n + (n-1)(75*2)/3 = 800
Solving for n = 14 plus a fraction
So, on the 14 increment, T will be swimming because n is even. But since n = 14 and change, T will be working
Therefore when K = 50, when T will be swimming rather then raking when the work is completed.