Can you arrange four 9's and use at most 2 math symbols, to make the total 100?

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

What has no start, end, or centre?

The husband and wife were jogging in the morning. To match every two steps of the husband, the wife required three steps. If Both of them start with the here right foot. After how many steps do their left foot be together?

When we see 2 but call 10?

Can you find the missing number in the third row?
35 20 14
27 12 18
5 2 ?

In a concert, Christina is performing a dance show with her group.
At 10:00, she and her crew were dancing in an absolutely straight line. At that time Christina was standing in 4th position from both the front and back end of the row.

What was the size of her crew?

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).

What makes this number unique: 8,549,176,320?

I am taken from a mine and shut up in a wooden case, from which I am never released, and yet I am used by almost every person. What am I?