I’m light as a feather, yet the strongest person can’t hold me for five minutes. What am I?

What is the four-digit number in which the first digit is one-third the second, the third is the sum of the first two, and the last is three times the second?

What four weights can be used to balance from 1 to 30 pounds?

John named his first son Alpha, second Beta, third Charlie and fourth Delta. What is the fifth son's name?

I came first on earth but second on the heaven.
I also came twice in a week but found just once in a year.
I stay away from months but you can find me in February.

What am I?

A man dies of old age on his 25 birthday. How is this possible?

Keyboard words are not in alphabetical order, Why?

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.

A man says, "Brothers and sisters, have I none, but that man's father is my father's son." Who is that man?

Below, you can see some coding:
January = 1017
February = 628
March = 1335
April = 145
May = 1353
June = 1064
July = 1074
August = 186

Now deciphering the way it has been coded, can you find out how September will be coded?