Solution:

27

Explanation:
16/2 = 9
8*3 = 24
24/2 = 12
12*3 = 36
36/2 = 18
18*3 = 54
54/2 = 27
27*3 = 81

Solution:

Fifteen Minutes.

After frying for five minutes, you can take out one steak and put the third one inside while turning the other one inside. After five more minutes, one steak is fried from both sides and you can take it out. Now put in the steak that we removed and turn the other one inside. After five more minutes, they both will also be fried from both sides.

Solution:

The woman told him to take out one nut each from the rest of the wheels and use them.

Solution:

The Bangladeshi seaman is the thief. This is because the Japanese flag cannot be identified as upside down as it is the same both ways. Thus he is just trying to escape the situation.

Solution:

7, 4, 6, 5, 8

Solution:

In the picture you can find the green matchsticks. We have moved them from the bottom and placed them in the middle. It was a bit tricky but now you have your desired result.

Solution:

This statement is true but only in a specific case i.e. if both of the siblings continue to live till the day the younger is as old as the elder one was during the time of their birth.

Solution:

A
D
C
A
B

Solution:

This can be done if you draw a five pointed star and place the balls on the corners and intersection points. See the figure to understand better.

Solution:

The brain teaser can be solved as shown in the image below.

Solution:

I + IX = X

The equation read from the other side becomes X = XI + I which is false.