What does this rebus puzzle means ?

You have two bottles of pills marked with labels A and B. The pills are identical. The doctor has asked you to take one A pill and one B pill daily. You cant take more or less than that.

While taking out the pills one day, you took out one pill from A and by mistake took out two from B. You have no idea which pill is which now.

You cant throw away the expensive pills. What will you do now?

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?

What work can one never finish?

You may enter, but you may not come in. I have space, but no room. I have keys, but open no lock. What am I?

I possess a head

I flaunt a tail

But I don't have mouth or legs

Can you find out who I am?

What goes through cities and fields, but never moves?

A mother is 21 years older than her child. In exactly 6 years from now, the mother will be exactly 5 times as old as the child.
Where's the father?

Through your logical capabilities, can you make 7 an even?

A finger goes in me. You fiddle with me when you're bored. The best man always has me first. What am I?