You need to measure the lengthof you driveway. which measuring tool would produce accurate results that would expect to be the same as those found by others a your hands span b a string cut to the length of the tip of you finger to the bottom of your palm c a meter stick with only centimeters d a ruler with millimeters and centimeters

C a meter stick with only centimeters

D a ruler with millimeters and centimeters

D would be to the nearest half milimeter. Take some time to measure with a 2 inch ruler. Would you really need to know the length to half a mil ?

connect the batteries in series and hope

it is given that trillions of microbes make up to 1% to 3% of the body mass.

let's take average of this percentage: 2%

consider the average mass of the human body as 70 kg.

then, trillions of microbes would have mass  

therefore, 100 trillion micro-organisms would weigh:

this is an approximate value and could change depending on the mass of the human body and percentage of the microbes present in it.

average mass per microorganism =