Solution:

Flipkart

Explanation:
Flipkart : 22664, Amazon: 22750 and Snapdeal: 23000

SnapDeal discount :
65000 - 42000 = 23000

Amazon 65% discount :
35/100 * 65000 = 22750

Flipkart 10% recursive discount:
After 1st 10% discount, Amount is 58500
After 2nd 10% discount, Amount is 52650
After 3rd 10% discount, Amount is 47385
After 4th 10% discount, Amount is 42646.5
After 5th 10% discount, Amount is 38381.85
After 6th 10% discount, Amount is 34543.665
After 7th 10% discount, Amount is 31089.2985
After 8th 10% discount, Amount is 27980.36865
After 9th 10% discount, Amount is 25182.331785
After 10th 10% discount, Amount is 22664.0986065

Solution:

11

Explanation:
We are looking at the numbers in the form of 5k +1 or 5k + 3
i.e The number ends in 1 or 3
If we jot down all such numbers, there are 16 in total:
1, 3, 11, 13, 21, 23, 31, 33, 41, 43, 51, 53, 61, 63, 71 and 73

Now, let us remove the ones that are not prime and we have the answer as:
3, 11, 13, 23, 31, 41, 43, 53, 61, 71 and 73

Solution:

9 - 8 + 76 - 5 + 4 + 3 + 21 = 100


Other ways of making number 100 (withiout using number 32)
98 + 7 + 6 - 5 - 4 - 3 + 2 - 1 = 100
98 - 7 - 6 - 5 - 4 + 3 + 21 = 100
9 - 8 + 76 - 5 + 4 + 3 + 21 = 100
98 - 7 + 6 + 5 + 4 - 3 - 2 - 1 = 100
98 + 7 - 6 + 5 - 4 + 3 - 2 - 1 = 100
98 + 7 - 6 + 5 - 4 - 3 + 2 + 1 = 100
98 - 7 + 6 + 5 - 4 + 3 - 2 + 1 = 100
98 - 7 + 6 - 5 + 4 + 3 + 2 - 1 = 100
98 + 7 - 6 - 5 + 4 + 3 - 2 + 1 = 100
98 - 7 - 6 + 5 + 4 + 3 + 2 + 1 = 100
9 + 8 + 76 + 5 + 4 - 3 + 2 - 1 = 100
9 + 8 + 76 + 5 - 4 + 3 + 2 + 1 = 100

Solution:

930

Explanation:
New number = Last number * multiplication factor (increased by 0.5 every time) + sum factor (increased by 5 every time)
10
10 * 0.5 + 5 => 10
10 * 1.0 + 10 => 20
20 * 1.5 + 15 => 45
45 * 2.0 + 20 => 110
110 * 2.5 + 25 => 300
300 * 3.0 + 30 => 930 , desired answer

Solution:

30%

Explanation:
√9%
=> √9/√100
=> 3/10
=> 30/100
=> 30%

Solution:

J = 1
O = 9
I = 6
N = 8
T = 3
(1+9+6+8+3)*(1+9+6+8+3)*(1+9+6+8+3) = 19683.

Solution:

It is possible when you write the numbers in their Roman form.
XI (11) - When you remove me from XI, it becomes X i.e. 10
IX (9) - When you remove me from IX, it becomes X i.e. 10

Solution:

Your friend's statement is actually true and it's not different from what you have answered.

25 - 55 + (85 + 65) = 25 - 55 + 150 = 120 = 5!
5! (factorial) = 5 * 4 * 3 * 2 * 1 = 120

Yes, that was a tricky question, quite capable to confuse anybody.

Solution:

19(snake) + 1(Echidna) + 80(Bird) Egg =>100 eggs.
Cost:
19*5 + 1 + 4 =>100 pence

Solution:

   9567
+ 1085
======
 10652