Baseball bat and ball cost $100. If the bat cost $99 more than the ball, what is the cost of each?

There are people and strange monkeys on this island, and you can not tell who is who (Edit: until you understand what they said - see below). They speak either only the truth or only lies.
Who are the following two guys?
A: B is a lying monkey. I am human.
B: A is telling the truth.

Twenty frogs are sitting on a log floating on the surface of a river. Two of them decide to jump off into the water.

How many frogs are there on the log at this moment?

Find the next number in the series?
2, 12, 36, 80, 150, 252, 392, _ ?

How many words can a pen with half refill write?

Living above a star, I do not burn
Eleven friends and they do not turn
I can just be visited in a sequence, not once or repeatedly
PQRS are my initials
Can you tell my name accurately?

You have a three-gallon and a five-gallon measuring device. You wish to measure out four gallons.

Name a key which is hardest to turn.

Can you quickly find which two matchstick figures are identical?

Pronounced as one letter,
And written with three,
Two letters there are,
And two only in me.
I am double, I am single,
I am black blue and grey,
I am read from both ends,
And the same either way.