So they can predict what happens next
The different types of microscopes are all necessary because not all experiments require the same level of magnification. For dissections low magnification is sufficient, so a dissecting microscope works very well, while for viewing single cells the 1000 fold magnification of a compound light microscope is more accurate.
22 because that how many days it will take for the exact moon shape to pass and it will then reappear.
12 times breathe give 240 ml of pure 
. Each breathe gives 20 ml of .
Let us consider, volume of air per breathe= x ml.
Pure from inhaled air= 
ml and Pure from exhaled air= 
ml.
Pure from inhaled and exhaled air= 20 ml
So, + = 20
Therefore, x = 55.5 ml
So, volume of air per breath= 55.5 ml.
