what does this picture(rebus) riddle means ?

What runs around the whole yard without moving?

If "P" means "-", "Q" means "/", "R" means "+", and "S" means "*" then find the value of the following:

21 Q 7 R 9 S 10 P 13

A Doctor always sneezes before the rain. Doctor sneezes, Will it rain?

I have branches, but no fruit, trunk or leaves. What am I?

When my father was 31 I was 8. Now he is twice as old as me. How old am I?

In the addition below, all digits have been replaced by letters. Equal letters represent equal digits and different letters represent different digits.
ABCABA
BBDCAA
ABEABB
ABDBAA
------- +
AAFGBDH
What does the complete addition look like in digits?

Complete the series by replacing "?" with the correct number.

ST ND RD TH '?'

Two men are in a desert. They both have packs on. One of the guys is dead. The guy alive has his pack open, and the guy who is dead has his pack closed. What is in the pack?

Known by all without exception, Forever here, for your protection, Sometimes strong, sometimes weak, Right after the night I come - hot and chic. And while millions of miles away, I always get to you, I find my way. No life around could do without me, Can you guess what I might be?