Solution:

There are twenty-four triangles in the given picture.

Solution:

Let us denote the number of boys as 'p' and the number of girls as 'q'.

The first statement says that each boy has equal numbers of brothers and sisters
(p - 1) = q
=> p - q = 1 ------- (a)

The second statement says that every girl has twice as many brothers as that of sisters
2 (q - 1) = p
=> 2q - p = 2 ------- (b)

By solving (a) and (b)
We get q as 3 and p as 4.

Therefore, there are 4 boys and 3 girls in the family.

Solution:

The bridge won't break.

When the car has travelled half of the bridge, that is 15km, the car must have used more than 300 grams of fuel. Therefore, the impact of bird's added weight will be zero literally.

Solution:

The rabbit is present in the left tusk of the elephant.

Solution:

The given words can be formed into the following words:
Recalculate
Hairball (or airbag)
Hydrolysis
Antibacterial
Guideline
Algorithm
Microscope
Keyhole

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.