Solution:

6

Explanation:
Key1: 3 attempts for 3 gates.
Key2: 2 attempts for remaining 2 gates.
Key3: 1 attempts for the last gate.

Solution:

797

Explanation:
797 is a prime number
79 is a prime number
7 is a prime number

Solution:

11

Explanation:
Tzu‑ying won 3 games
V.Sindhu must win 3(to balance 3 games she lost) + 5 games(required for min 50$) = 8 games
Total Games = 3 + 8 = 11 games.

Solution:

==== 65 ==== 35 ====
== 34 === 31 === 4 ==
= 10 == 24 == 7 == -3 =

Solution:

The poison was not in pills but in water.

Solution:

8 Steps

Explanation:
Steps------2L Gallon-------5L Gallon
A-------------12-------------0
B-------------07-------------5
C-------------07-------------0
D-------------02-------------5
E-------------02-------------0
F-------------00-------------2
G-------------12-------------2
H-------------09-------------5

Solution:

Phoebe broke the machine and Monica is telling the truth.

> Rachel says Monica did it
If this is true, then the last statement must be true as well.

> Monica says Rachel is lying

> Phoebe says she did not.
If this is true, then one of the first two statements must be true as well.

Solution:

3rd.

Explanation:
Rule: Take the bottom row, flip it, and put it on the top.

Solution:

When blind man "Grandpa" opened his bandages, the train must be passing through the dark tunnel. The man thought he was still blind and hence commit suicide.

Solution:

On phone, using pause button, the teller messaged to her mother "Emergency mother, call help".

Explanation:
all Except one in bold is paused by the teller.
Is there an emergency mother, Call me when you reach home and I will help you with the dinner.