Solution:

3.75 hours

Explanation:
While you can solve it as you like, a simple mathematical equation can be used to find out.
Let M be the amount of petrol initially.
Let N be the time for which they drove.
According to the question, the amount of petrol used by first car in N hours = MN / 4
The amount of petrol used by second car in N hours = MN / 5
Hence, the amount of petrol left in the first car = (M - MN / 4)
The amount of petrol left in the second car = (M - MN / 5)
AS per the details given in the question, we can form the below equation:
M - MN / 5 = 4(M - MN / 4)
N = 15 / 4 or 3.75 hours.
Hence, both the drivers have driven the car for 3.75 hours at that particular time.

Solution:

There are 3 fruits (1 grapes, 1 apples, and 1 oranges).

Solution:

The competition was held on 11 November 2013. The logic is simple. In America, the dates are mentioned as Month/Day/Year and in Britain, dates are written as Day/Month/Year. But on 11 November 2013, the date and month will be the same. And thus both will write in the same manner i.e. 11/11/2013. If it would have been any other date, the evaluators would have been able to identify it.

Solution:

Sansa has the siamese (conjoined) twin sister.

Solution:

There is no reason whatever why the customer's original deposit of Rs.100 should equal the total of the balances left after each withdrawal.
The total of withdrawals in the left-hand colum may equal Rs.100, but is is purely coincidence that the total of the right-hand column is close to Rs.100.
Let us show another example, but starting with Rs.200 in the bank:
Withdrawals Balance left
Rs.50 Rs.150
Rs.25 Rs.125
Rs.10 Rs.115
Rs.8 Rs.107
Rs.5 Rs.102
Rs.2 Rs.100
Rs.100 Rs.699
Moral of this story? Don't Total Balances

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:

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

Solution:

The password is U472BMT.

Read aloud the line and you will sound something like "U Four Seven 2 B M T".

Solution:

99 matches.

The number of matches will always sum up to one less than the number of players in a knock out tournament. You may calculate it in any manner. Thus 99 matches were played.

Solution:

I filled a glass full of water and held it over my head for 20 minutes.

Solution:

10,15,9,20,12

Explanation:
The score obtained on the first throw is 10.
The score obtained on the second throw is 15.
The score obtained on the third throw is 9.
The score obtained on the fourth throw is 20.
The score obtained on the fifth throw is 12.