Replace the question mark with the number below given a simple math problem.

I have two sand hourglasses:
1. A 7 minute one and
2. An 11-minute one.

Using just these 2 sand hourglasses, how can I measure time as 15 minutes?

Spot what is wrong here in below Picture?

Eight of us go fourth, not back, to protect our king from an attack. What are we?

A man who was outside in the rain without an umbrella or hat didn’t get a single hair on his head wet. Why?

What are the next two letters in the following series and why?
W A T N T L I T F S _ _

*Hint: Check Puzzle Title

Which statement is true out of the following?
One statement here is false.
Two statements here are false.
Three statements here are false.

The answer I give is yes, but what I mean is no. What was the question?

A crime was committed at baker street. Ibrahim Dakota who was shot in the stomach was the main suspect. Sherlock questioned the suspect. The conversation started as:
Sherlock: What's your story, Ibrahim?
Ibrahim: I was walking around baker street and suddenly a man from the back shot me. I ran as fast as I could to save my life".
Sherlock: That is enough (and ask the police to arrest him).

Why does Sherlock think he is the murderer?

Using Only Five 5's and any mathematical operator make sum as 37