Which tank will fill first?

Which number should replace the question mark?

I go up and I go down.
I go up towards the beautiful sky and down toward the green ground.
I am present tense.
I am past tense too
Children love me.

Who Am I?

Why 1729 is a magic number? Answer Logically.

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?

Can you count the number of triangles in the picture below?

A family is trapped in a jungle. There is a bridge which can lead them to safety. But at one time, the bridge can only allow two people to pass through. Also, all of them are afraid of the dark and thus, they can't go alone.

Father takes 1 minute to cross, the mother takes 2 minutes, the son takes 4 and the daughter takes 5 minutes. While crossing the time taken will be according to the slower one. How can they all reach the other side in the minimum possible time?

No one wants to have it, but if one got it, he does not want to lose it. What is It?

How many times can you subtract the number 5 from 25?

You have a basket containing ten apples. You have ten friends, who each desire an apple. You give each of your friends one apple.
Now all your friends have one apple each, yet there is an apple remaining in the basket.
How?