Solution:

16/81

Explanation:
It is a question of geometric progression but we can solve it step by step as well in case you are not aware of the formula.

At first bounce
The height at which the ball would have reached = 2/3 of the original height from which it was dropped.

At second bounce
The height at which the ball would have reached = 2/3 * 2/3 of the original height from which it was dropped.

At third bounce
The height at which the ball would have reached = 2/3 * 2/3 * 2/3 of the original height from which it was dropped.

At fourth bounce
The height at which the ball would have reached = 2/3 * 2/3 * 2/3 * 2/3 of the original height from which it was dropped.

Now, 2/3 * 2/3 * 2/3 * 2/3 = 16/81

Therefore, 16/81 of the original height from which the ball was dropped is the required fraction height.

Solution:

They use the bricks and dirt from the tunnel to stand on it.

Solution:

Put one black rock in one sack and put all the rest in the other one. In such manner you will get about 3/4 probability of surviving.

Solution:

Solution can be verified from the picture below.

Solution:

TIF56

Explanation:
The password is formed as:
T (5th letter of Shruti)
I (5th letter of Arshika)
F(1st letter of Friday)
5(5th day of week)
6(Length of Friday)

Similarly, we will pick the 1st letter for Monday and 3rd letter for Wednesday.

Solution:

The answer is 'R'

It represents the gear stick. The number 1-5 represents gears and the last one thus should be reverse i.e. R.

Solution:

The mules is moving in circular path and hence outside legs travels more distance than inner legs.

Solution:

For this answer is 3^0, 3^1, 3^2... That is 1,3,9,27,81,243 and 729.

Solution:

30,450 miles.

Explanation:
For each 5 miles driven using this rotation, each tire will lose (2/29000)+(2/21000) of its tread.So, suppose we drive 5*N miles like this. Then, each tire will lose 2*N*((1/29000)+(1/21000)) of its tread. We wish to determine N so that the latter expression gets to be 1, representing all of each tire's tread. That happens when N=6090, which is when 5*N (the total miles driven) is 30,450.

Solution:

Since the knife was in her hand which implies that she was planning to kill her husband "Inspector Montalbano".

Solution:

The guard and the prisoner cross the river
The guard comes back
The guard and the girl cross the river.
The guard and the prisoner comes back.
The mother and the girl cross the river.
Mother comes back
The mother and the father cross the river
Father comes back
The guard and the prisoner cross the river
Mother comes back
The father and the mother cross the river
Father comes back
The father and the boy cross the river
The guard and the prisoner comes back
The guard and the boy cross the river
The guard comes back
The guard and the prisoner cross the river.