An express train takes 3 seconds to enter the tunnel which is 1 km long.
If it is travelling at 120 km an hour, how long will it take to pass completely through the tunnel?

They came out at night, without being called.
They lost at day, without being stolen.
Who are they?

Two in a corner, one in a room, zero in a house, but one in a shelter. What am I?

I have cities, but no houses. I have mountains, but no trees. I have water, but no fish. What am I?

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?

Only one colour, but not one size,
Stuck at the bottom, yet easily flies.
Present in sun, but not in rain,
Doing no harm, and feeling no pain.
What is it?

Look at the below sequence of letters and tell us what the next letter should be:

O T T F F S S ?

What has 88 keys?

John is the son of Jacob.
So,
Jacob is the_____of John's father?

What does this mathematical rebus means ?