Solution:

The sword could not have the words 'World War I' engraved on it. At that time, only one world war had taken place. No one knew that a second was to happen in future. Thus if it was engraved, the mention of the number was impossible.

Solution:

The three numbers are:
-3, -1 and 1.

Solution:

Take both the ropes. Now light the first rope from both the ends. Light the second rope from just one end. In thirty minutes, the first rope will burn fully. At this point of time, the second rope will be left exactly half and you have to light it from the second end now. It will take half of the actual time (thirty minutes) to burn now i.e. fifteen minute.

Thirty Minutes + Fifteen minutes = Forty Minutes

Solution:

The missing letter on left is P and the missing letter on the right is C. The word starts from the missing letter C and forms the word champion.

Solution:

Yes, this can be possible if the match was between two female boxers.

Solution:

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

Solution:

Give Up

SLOW when read down gives us Slow Down.
GIVE when read upwards gives us Give Up.

Solution:

He cannot marry his widow's sister in any country. This is because if his wife is a widow, he is already dead.

Solution:

The question tells us that a taxi driver was going the wrong way. It is however not mentioned that he was driving the cab. As per the question, it is evident that he was on foot and that is why the police officer did not fine him.

Solution:

9

Explanation:
2 < 3 < 5
To find out the required number of candies, take one in place of the least number (i.e. take one mango candy) and then add all the greater numbers (i.e. three strawberry and five pineapple candies) to it.

Required number of balls = 1 + 3 + 5 = 9.