Replace the question mark with the correct number in the below-given picture?

There are 2 people near the river and both of them want to get on the other side. The boat can only take one of them. But they got across.
How?

Krish is 45 years old and his mother Crishtina is 73 years old.

Can you find out how many years ago, his mother was three times his age?

In my garden, I have many trees but only one of them is the mango tree. In these mango trees, there are some mangoes(as expected).

But after a strong wind, there are neither mangoes on the tree nor on the ground. Explain?

You have a 12 liters jug full of water. You have two empty 8 liters and 5 liters jug. How can you divide the water into two equal parts using these jugs?

What has 88 keys?

In the given figure, move three matchsticks so that the resulting figure contains two rectangles.

What Does this text mean:

important=important

If 1+9+8=1, what is 2+8+9?

You are given a cube that is made with the help of 10x10x10 smaller cubes summing up to a total of 1000 smaller cubes. You are asked to take off one layer of the cubes.
How many remain now?