depends on how many leaves and the size of the lake
depends how much of the lake was already covered with the lilly pads
10 days (or 9 1/2 days if it's a lateral thinking question!)
it depends on whether the lily pads get eaten by wildlife
Impossible to answer without knowing the size of the lake and the original size of the patch
5.   This is another one of those damn trick questions !
i would say 10 but its a trick question and my maths is not good to analyse this question in detail
i would say 10 , already its probably not !
Dont know as you didnt give the lake size
19 days for the first half, one day for the last half