What has many keys but can’t open a single lock?

What number does the below three word/phrase identify and why?
1. Deck
2. Year
3. Singing in the Rain

A finger goes in me. You fiddle with me when you're bored. The best man always has me first. What am I?

When I get multiplied by any number, the sum of the figures in the product is always me. What am I?

A shepherd had 18 sheep, out of which, all but ten died.

Can you tell us how many sheep was he left with?

If you remove one from eleven, it becomes ten. If you remove one from nine, it becomes ten.

How is this possible?

No matter how little or how much you use me, you change me every month. What am I?

Sally lives in a place where six months of the year is mild summer and the temperature drops significantly the other six months. She owns a lake where there is a small island. She wants to build a house on the island and needs to get materials there. She doesn’t have a boat, plane, or anything to transport them to the island. How does Sally solve this problem?

How many cubic feet of dirt are in a hole of one foot deep, three feet long, and two feet wide?

If an earthquake is 1 point higher on the Richter Scale than another earthquake which is actually 10 times stronger, how much stronger would an earthquake be if it was just half a point higher on the Richter scale?