A convex lens of power 3 D is held in contact with a concave lens of power -1 D. A parallel beam of light is made to fall on the combination. At what distance from the
combination will the beam get focused?

answer: aliens exist but, they're being kicked out of our planet for not looking like us homosepians(humans) : 3

explanation:

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 =