What does this simple rebus mean?

Can you find out the missing number?

? 4 5 3 5

9 5 7 10 3

Twenty frogs are sitting on a log floating on the surface of a river. Two of them decide to jump off into the water.

How many frogs are there on the log at this moment?

What do you get if you add 2 to 100 four times?

A girl has as many brothers as sisters, but each brother has only half as many brothers as sisters. How many brothers and sisters are there in the family?

Astrology starts with the alphabet A, Biology starts with B, Psychology with P and Limnology with L.

Can you find an "ology" that begins with a P?

A tree doubled in height each year until it reached its maximum height over the course of ten years. How many years did it take for the tree to reach half its maximum height?

Two batsman each on 94 runs. Seven runs needed to win in last 3 balls. Both make 100*. How?

There's one "sport" in which neither the spectators nor the participants know the score or the leader until the contest ends.

What is it?

Given below is simple addition with a defined pattern pattern:
7 + 7 = 2
8 + 8 = 4
8 + 5 = 1
6 + 9 = 3
10 + 11 = 9

Can you analyze the pattern and find out the answer for:

4 + 9 = ?