Can you find out the next digit in the following series ?

0, 0, 1, 3, 2, 6, 3, 9, 4, 12, 5, ?

Two friends decide to get together; so they start riding bikes towards each other. They plan to meet halfway. Each is riding at 6 MPH. They live 36 miles apart. One of them has a pet carrier pigeon and it starts flying the instant the friends start traveling. The pigeon flies back and forth at 18 MPH between the 2 friends until the friends meet.

How many miles does the pigeon travel?

Take number 1000 and then add 20 to it.
Now add 1000 one more time.
Now add 30.
Now add 1000 one more time.
Now add 40.
Now add 1000 one more time.
Now add 10.

What is the total?

What is always in front of you but can’t be seen?

I have no doors but I have keys, I have no rooms but I have space, you can enter but you can’t leave! What am I?

What's the only room from which no one can enter or leave

How will you measure 15 minutes using two hourglasses of 7 minutes and 11 minutes respectively?

Can you find the next number in the below sequence
3 , 7 , 10 , 11 , 12 , 17 ?

What goes up but never comes down?

You need to climb ten stairs. At every stair, you can either take one step up or you can jump two steps up.

In how many different ways you can climb 10 stairs?