It walks on 4 when its young, walks on 2 when it's older, and walks on 3 when its very old?

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?

Find The Next Number In The Sequence

30 10 15 13 0 16 -15 ?

The person who makes it has no need for it. He who purchases it does not use it. The person who does use it does not know they are. What is it?

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

What is the next shape from answers A, B, C, and D figure?

One is to three as three is to five and five is to four and four is the magic number.
What is the pattern?

A dying old man wants to divide his entire land between his only two sons. Since his only wish is to treat them as equal as both of them have been too good to him, he wants to divide his land equally between them. The problem is that the land is significantly irregular in shape and thus there is no choice of cutting them into two equal halves.

Can you help him divide the land in a manner that both of his sons will be happy?

Can you fill the blank with the correct number?

6 30 870 756030 _____

A large water tank has two inlet pipes (a large one and a small one) and one outlet pipe. It takes 3 hours to fill the tank with the large inlet pipe. On the other hand, it takes 6 hours to fill the tank with the small inlet pipe. The outlet pipe allows the full tank to be emptied in 9 hours.

What fraction of the tank (initially empty) will be filled in 0.64 hours if all three pipes are in operation? Give your answer to two decimal places (e.g., 0.25, 0.5, or 0.75).