After a bit of thought, I came to the conclusion that it's better if we stick to riddles/teasers that can have a definite answer. So let me write my point of view on the last matter and give a more solid riddle to solve.

On the previous problem we had two conditions to fulfill.

1) Get a head on the first toss.

2) Get a tail at least once.

We tossed 3 times, so all the possible outcomes would be 2³, or in detail,

Head Head Head

Head Head Tail

Head Tail Head

Head Tail Tail

Tail Head Head

Tail Head Tail

Tail Tail Head

Tail Tail Tail

Only 3 out of 8 fulfill both conditions. Head Head Tail, Head Tail Head and Head Tail Tail. So the chances of having a head first and then at least one tail is 3/8, or 37,5%.

Now for the more solid one. I want you to find the smallest number with the following properties.

When divided it by 2, the remainder is 1.

When divided it by 3, the remainder is 2.

When divided it by 4, the remainder is 3.

When divided it by 5, the remainder is 4.

When divided it by 6, the remainder is 5.

When divided it by 7, the remainder is 6.

When divided it by 8, the remainder is 7.

When divided it by 9, the remainder is 8.

When divided it by 10, the remainder is 9.