Figures don't lie but liars sure can figure.
This is not a trick question: If you have a chunk of green firewood that is 50% moisture and dry it down to 20% moisture, how much moisture did you lose?
Write down your guess.
Let's assume you have a piece of that green wood in your hand and it weighs exactly one pound. Since it is 50% moisture, that means that it is a half-pound of water and a half-pound of anhydrous wood.
Dried to 20% moisture it still has a half-pound of anhydrous wood but now it is down to 0.125 pounds of water.
Yeah, counter-intuitive. The chunk now weighs 0.625 pounds and the water-weight is 0.125. 0.125/0.625 = 20% moisture.
The water-weight dropped from 0.5 to 0.125 pounds or a reduction of 75% of the original amount of water.
Why is that important?
It is important because when you are burning wood you must first invest heat to bring the chunk up to about 500 degrees before it will catch fire. You must effectively boil off all of that water before the dry-weight starts contributing any heat at all.
To convert water from liquid to vapor gobbles up a huge amount of energy.