What is so fragile that saying its name breaks it?

A rubber ball keeps on bouncing back to 2/3 of the height from which it is dropped. Can you calculate the fraction of its original height that the ball will bounce after it is dropped and it has bounced four times without any hindrance ?

Begin with a word, five letters to my name,
Remove the first and last but I am the same
Take out my middle and still, I remain.
What word am I?

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

How many times can you subtract the number two from the number fifty?

Pronounced as one letter,
And written with three,
Two letters there are,
And two only in me.
I am double, I am single,
I am black blue and grey,
I am read from both ends,
And the same either way.

If six children and two dogs were under an umbrella, how come none of them got wet?

I have branches, but no fruit, trunk or leaves. What am I?

Using the clues below, what four numbers am I thinking of?

The sum of all the numbers is 31.
One number is odd.
The highest number minus the lowest number is 7.
If you subtract the middle two numbers, it equals two.
There are no duplicate numbers.

Cristina was born in 1888. She just had her 30th birthday today how did that happen?