What has many keys but can’t open a single lock?

Can you write down eight eights so that they add up to one thousand?

A father's child, a mother's child, yet no one's son.

Who am I?

Replace the 'X' with any mathematical symbol to make the expression equal to 111.

18 X 12 X 2 X 3 = 111

In two decks of cards, what is the least amount of cards you must take to be *guaranteed* at least one four-of-a-kind?

Replace the question mark with the correct number.

How many times in a given day, minutes and hour clock comes in a straight line ?

You have to put a letter on the following to make it a meaningful word. The only challenge is that you can't use 'E'.

S E Q U E N C _

What does the below rebus riddle means?

There are 100 bulbs in a room. 100 strangers have been accumulated in the adjacent room. The first one goes and lights up every bulb. The second one goes and switches off all the even-numbered bulbs - second, fourth, sixth... and so on. The third one goes and reverses the current position of every third bulb (third, sixth, ninth? and so on.) i.e. if the bulb is lit, he switches it off and if the bulb is off, he switches it on. All the 100 strangers progress similarly.

After the last person has done what he wanted, which bulbs will be lit and which ones will be switched off?