What does this rebus riddle means ?

There is a shop where written:
Buy 1 for $1
10 for $2
100 for $3
I needed 999 and still only paid $3. How could this be financially viable for the shop-keeper?

John, Jack and Jill are in a desert. John doesn't like Jill and hence decides to murder him. He poisons the water supply of Jill. Since it is a desert area, Jill must drink or he will die of thirst.

Jack does not know of the actions of John and also decides to murder Jill. To succeed in his ill motives, he removes the water supply of Jill so he dies of thirst.

Jill dies due to thirst. Who murdered Jill?

A word I know has six letters it contains, remove one letter and 12 remain. What is it?

I ask Joseph to pick any 5 cards out of a deck with no Jokers.

He can inspect then shuffle the deck before picking any five cards. He picks out 5 cards then hands them to me (Jack can't see any of this). I look at the cards and I pick 1 card out and give it back to Joseph. I then arrange the other four cards in a special way, and give those 4 cards all face down, and in a neat pile, to Jack.

Jack looks at the 4 cards i gave him, and says out loud which card Joseph is holding (suit and number). How?

The solution uses pure logic, not sleight of hand. All Jack needs to know is the order of the cards and what is on their face, nothing more.

Take 9 from 6, 10 from 9, 50 from 40, and leave 6.

How Come ??

A shepherd had 18 sheep, out of which, all but ten died.

Can you tell us how many sheep was he left with?

A Doctor always sneezes before the rain. Doctor sneezes, Will it rain?

I have a hole in my back and legs I lack.
I live where I can’t breathe and I eat without teeth.
What am I?

Can you find the missing letter in the sequence?
S - T - I - L - ? - T - F - Y - C