Instead nick hands the rope with the scale to his friend barney, who stands on the ground. barney pulls on the rope so that the spring scale again reads 320 n. what is nick's acceleration now, again using upward as positive.

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 =