Solution:

Pick 1st.

Explanation:
> Take 1 coin
> Pick the opposite number of coins from the other soldier i.e if other soldier pick 1 coin, you pick 2 and if he picks 2 coins you pick one
> After 15 moves, coins remaining will be 23 - 1 - 7(2+1) = 1
> The other solider need to pick the last and he will loose.

Solution:

2nd Feb

Explanation:
a.b X a/b = 1
2.5 x 2/5
= 5/5
= 1

Solution:

One of 57620 or 57628 must be the secret code.

Explanation:
Hint-1: 79314
Only 7 is there and in wrong

Hint-2: 95643
6 is in the right position while 5 is not

Hint-3: 57319
5 and 7 are in the right position

Sum Hint: A + B + C + D + E = D*10 + E
CaseA - 57620
5 + 7 + 6 + 2 + 0 = 2 * 10 + 0
20 = 20

CaseB - 57628
5 + 7 + 6 + 2 + 8 = 2 * 10 + 8
28 = 28

Solution:

7 Trips

Explanation:
Send 2+5+9 = 16
Bring back 9
Send 3+4+9 = 16
Bring back 9
Send 1+7+8 = 16
Bring back 1
Send 1+6+9 = 16

Solution:

CANNOT BE CRACKED

Explanation:
This code can be cracked with the help of table below.
i.e
31 => 3rd row and 1st column => C
11 => 1st row and 1st column => A
33 => 3rd row and 3rd column => N
and so on....

Solution:

Murder.

Explanation:
1. There are signs of the struggle in the room as the clock is broken.

2. Two water glasses in the room indicate the presence of two people which also suggest that the killer is known to the victim.

3. There are a book and a pen on the bed which indicates that the dead person was reading and a suicide note was written from another pen which seems to be planted.

4. The man crutches are too far from the man.

Solution:

Either Rain Cloud Or Air

Explanation
=== Rain Cloud ===
I don't have a mouth but can roar - Thunder
I don't have eyes but can cry - Rain
I am really good - Rain is good
but bad sometimes - Storms
Without me, all will die - rain is the necessity for agriculture and human being

=== Air ===
I don't have a mouth but can roar - Wind
I don't have eyes but can cry - Moisture
I am really good - Rain is good
but bad sometimes - Hurricanes
Without me, all will die - Oxygen

Solution:

I Over Ate

Explanation:
Check the mathematical solution on the image below.
Also, 8 in 2018 resembles a fat person.

Solution:

The cowboy can fit the horses as shown below.

[T] [E] [N] [H] [O] [R] [S] [E] [S]

Solution:

Pour 3 lumps on cup-1 and cup-3 and 4lumps on cup4 and place them as shown in the picture.

Explanation:
Now,
Cup-1 got three sugar lumps
Cup-3 got three sugar lumps
Cup-2 got three seven lumps (3 of cup-1 and 4 of its own)