Solution:

See the picture for the answer. Don't worry if you have a different answer; this question can be solved with different numbers. However, do post your answer in the comments.

Solution:

C

Explanation:
Check the image.

Solution:

3

Explanation:
Fernando + Alonso + McLaren = 6
Fernando x Alonso = 2
Alonso x McLaren = 6

Given.
Fernando x Alonso = 2
Alonso x McLaren = 6

Rewriting Both equations in terms of Alonso,
Fernando = 2/Alonso
McLaren = 6/Alonso

Replacing above values in equation "Fernando + Alonso + McLaren = 6"
2/Alonso + Alonso + 6/Alonso =6
(2 + Alonso^2 + 6)/Alonso = 6
8 + Alonso^2 = 6Alonso
Alonso^2 - 6Alonso + 8 = 0
(Alonso - 4) (Alonso - 2) = 0

Therefore;
Alonso = 4 or 2

Let's take value of Alonso as 2
Fernando = 2/2 = 1
McLaren = 6/2 = 3

Therefore;
McLaren x Fernando = 3 x 1 = 3

Solution:

Rashid's son-1: 1 11 21 31 41 51 61 71 81
Rashid's son-2: 2 12 22 32 42 52 62 72 73
Rashid's son-3: 3 13 23 33 43 53 63 64 74
Rashid's son-4: 4 14 24 34 44 54 55 65 75
Rashid's son-5: 5 15 25 35 45 46 56 66 76
Rashid's son-6: 6 16 26 36 37 47 57 67 77
Rashid's son-7: 7 17 27 28 38 48 58 58 78
Rashid's son-8: 8 18 19 29 39 49 59 69 79
Rashid's son-9: 9 10 20 30 40 50 60 70 80

Solution:

Nightmare.

Explanation:
(K)night + mare (A mare is the female of a horse)

Solution:

Day 1:
Alibaba Give 1kg gold bar.

Day2:
Now Alibaba gives 2kg gold bar and takes back 1kg gold bar back.

Day3:
Alibaba gives 1kg gold bar.

Day4:
Alibaba gives 4kg gold bar and take back 1kg gold bar back

Day5:
Alibaba gives 1kg gold bar.

Day6:
Alibaba gives 2kg gold bar and takes back 1kg gold bar back.

Day7:
Alibaba gives 1kg gold bar.

Solution:

Difference 1
Toy plane direction is different.

Difference 2
On the clock, number 1 & 2 is missing.

Difference 3
The colors of lamp's light is changed.

Difference 4
The ribbon on the gift is missing.

Difference 5
Duck is added in the gift section.

Solution:

It can be done in 8 moves as shown in the animated image below.

Solution:

The brain teaser can be solved as shown in the image below.

Solution:

+ 9 6 2 3 3
+ 6 2 5 1 3
===========
1 5 8 7 4 6