Solution:

The nail would be at the same height since trees grow at their tops.

Solution:

Tilt the Mug until the coke barely touches the lip of the Mug. If the bottom of the Mug is visible then it is less than half full. If the Mug bottom is still completly coverd by the coke, then it is more than half full.

Solution:

Forty.

The number of decks is irrelevant; the answer is the same if one or one-hundred decks are used.

Any card drawn will be a A,2,3,4,5,6,7,8,9,10,J,Q, or K, so there are 13 possibilities each time a card is drawn.

The fastest way to draw a four of a kind is if the first four cards all have the same 'value.' The slowest way, which provides the solution, is to first draw 13 three of a kinds, and then one more card.

Since 13 x 3 + 1 = 40, if 40 cards are drawn it is guaranteed that those forty cards contain at least one four of a kind.

Solution:

Cold

Solution:

When you mix bleach and ammonia [found in most cleaning products] it creates a deadly gas that can kill.

Solution:

An Echo

Solution:

The peahen lays eggs

Solution:

22 times

am
12:00
1:05
2:11
3:16
4:22
5:27
6:33
7:38
8:44
9:49
10:55

pm
12:00
1:05
2:11
3:16
4:22
5:27
6:33
7:38
8:44
9:49
10:55

Solution:

A man, who crawls on all fours as a baby, walks on two legs as an adult, and walks with a cane in old age.

Of course morning, noon, and night are metaphors for the times in a man's (person's) life. Such metaphors are common in riddles. There were two Thebes, apparently this Thebes was the one in Greece. And this Sphinx was apparently not the one at Giza, in Egypt.

Solution:

Only twenty-three people need be in the room, a surprisingly small number. The probability that there will not be two matching birthdays is then, ignoring leap years, 365x364x363x...x343/365 over 23 which is approximately 0.493. this is less than half, and therefore the probability that a pair occurs is greater than 50-50. With as few as fourteen people in the room the chances are better than 50-50 that a pair will have birthdays on the same day or on consecutive days.