Solution:

The answer to this question lies in the second book of the series titled as - The Chambers of Secrets. The phrase 'I Am Lord Voldemort' can be treated as an anagram and re-written as 'Tom Marvalo Riddle'. Further in the book, it is explained that Voldemort changed his name because he wanted to distance himself from his father and muggles.

Solution:

The number missing on the left is 8 and the one on right is 7.

Explanation:
The pattern:
The number in the center of triangle is the square root of the sum of the numbers sitting outside on the corners.

Thus,
10 + 22 + 4 = 36
Square Root of 36 = 6

In the same manner:

10 + 42 + 12 = 64
Square Root of 64 = 8

12 + 22 + 15 = 49
Square Root of 49 = 7

Solution:

(210 + 6)

Explanation:
If you add the numbers, you will find that they add up to be 8, 27, 64 and 125.
8 = 2^3
27 = 3^3
64 = 4^3
125 = 5^3

Thus the next sum should be 6^3 = 216.

Since 6 has been added in each set, the first number will be (216 - 6) = 210.

Hence, the missing set will be (210 + 6).

Solution:

This can be possible. They are not twins but triplets.

Solution:

It can be achieved as it is shown in the figure.

Solution:

They used the planks in the manner that is shown in the figure.

Solution:

If you build a house on the South Pole, all of its walls will face towards North.

Solution:

3 3/4 hours

Explanation:
Suppose that the amount of petrol in each of the cars in the beginning was M.
Now, suppose that they drove for X hours.

In that case, the amount of petrol used by one car in X hours will be = M*X /4
The amount of petrol used by the other car will be = M*X/5

Therefore, the petrol left in one car = M - M*X / 4
Petrol left in the other car = M - M*X / 5

Now, according to the question,
M - M*X / 5 = 4 (M - M*X / 4)
=> X = 15 / 4 = 3 3/4 hours.

Therefore Murphy and Cooper drove for 3 3/4 hours.

Solution:

doughnut

Solution:

98

Explanation : ab + a(a-1)
7 * 8 + 7(7-1)
= 56 + 42