How can you take 2 from 5 and leave 4?

What number comes next in this sequence:
7 8 5 5 3 4 4 _

A tree doubled in height each year until it reached its maximum height over the course of ten years. How many years did it take for the tree to reach half its maximum height?

Find out a multi-digit number that if multiplied by the number 9 or any of its multiplications products (i.e. 18, 27, 36, 45,..) will result in the multiplication factor repeated (n) number of times.

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?

I sleep during the day and fly at night, but I have no feathers to aid my flight. What am I?

The product of three consecutive numbers is 7980.
Then the sum of these consecutive numbers would be?

What is the next number in this matchsticks series riddle?

You can hear me, but you can't touch or see me.

What am I?

Do You See It?