Scientific notation

Question

A sample of microbes weighs 50 mg. There are approximately 2.5 * 10^6 microbes in a sample. What is the approximate mass of each microbe expressed using scientific Notation in grams. Show working Please. Thank you 

Answer 1

It helps to use the unit factor method, also referred to as dimensional analysis.  This is where you arrange the values in such a way that the units you don't want cancel, leaving you with the units you do want.  Thus,...

50 mg x 1 g/1000 mg x 2.5x10⁶ microbes = 2.0x10^-8 g/microbe

Note that mg cancel to give grams, and then you are left with grams/microbe.

Done another way.

Converting mg to grams:  50 mg x 1 g/1000 mg = 0.05 g = 5.0x10^-2 g 

5.0x10^-2 grams/2.5x10⁶ microbes = 2.0x10^-8 grams/microbe