A70-kilogram hockey player skating east on an
ice rink is hit by a 0.1-kilogram hockey puck
moving toward the west. the puck exerts a
50-newton force toward the west on the player.
determine the magnitude of the force that the
player exerts on the puck during this collision.
[1]

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 =