2, 3, 5, 9, 17, _ What is the next number in the sequence?

If I remove one from eleven it becomes Ten and if I remove one from nine also becomes Ten. How?

Decode below three cipher riddles:

26 L of the A
7 D of the W
1000 Y in a M

A sundial has the fewest moving parts of any timepiece. Which has the most?

A worker is to perform work for you for seven straight days. In return for his work, you will pay him 1/7th of a bar of gold per day. The worker requires a daily payment of 1/7th of the bar of gold. What and where are the fewest number of cuts to the bar of gold that will allow you to pay him 1/7th each day?

Count the number of triangles in the below picture?

The doctor prescribed you to take one pill from the bottle every half an hour. The bottle is now left with only three pills.

How long do you think you have before you run out of pills?

One night, a woman receives a call from the police. They tell her that her husband was murdered and that she should come to the crime scene as soon as possible. The woman drops the phone, shocked, and drives 20 minutes to the crime scene. As soon as she reaches the crime scene, the police arrest her and she is convicted of murder. How do the police know she committed the crime?

A few friends are enjoying their sea voyage in a boat full of apples. On the way, they felt hungry and thus decided to eat the apples. Together, they ate two dozen of apples. When they have eaten the apples, will there be any change in the water level?

I am a seven-letter word but if you remove four of my letters I will have one left. What word am I?