Solution:

These types of problems are known as linear relation problems. If you know how to solve, they re pretty easy.

Bruce takes 11s to run y yards
Thus he will cover 1 yard in 11/y seconds

Now 1 yard = 11/y seconds
Multiplying both sides with x
We get, x yards = 11x/y seconds

Thus Bruce will take 11x/y seconds to cover the distance x.

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:

Just One!

example
If u get Blue rock with label as "blue+red" => this is red as all labels are wrong.
In this way u can logically solve this puzzle.

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:

If you see the picture, they formed a pentagonal shape and achieved the required.

Solution:

Solution can be verified from the picture below.

Solution:

Steps:
1) Light fire on first bar from both the ends and second bar from one end.

2) After 30 seconds(when first bar gets completely burned out) , burn the second bar from second end as well.

3) When second run completely gets burned , you know its 45 seconds.

Solution:

Playing chess

Game needs two players so Brother-8 is playing chess with Brother-2

Solution:

f the last elf is taking some time to answer the question then it shall mean that the elf's before him are all wearing distinct coloured hats. However sufficient time shall be given to the last elf to give the answer.
If he views the similar coloured hats in front of him , he shall quickly tell the answer

Solution:

It can be down as shown below.

Solution:

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