Atabletennis ball strikes an at-rest bowling ball. the table tennis ball is
moving with moderate speed. what is the likely result?

-- The table tennis ball bounces back with virtually its entire original speed.

-- The bowling ball rolls forward, so slowly that only complex expensive laboratory equipment can detect and measure its speed.

-- Once again, momentum is conserved !

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 =