The grocery store is 20 miles away from where you live. You drive your
car and it takes .5 hours to get there.
What was your rate of speed?

40mph

Explanation:

20miles  .5 miles away if you go 20 mph you get there in a hour soo if you double to 40 mpg you get there in 0.5

40 mph

Explanation:

you went 20 miles in half a hour, multiply twenty by 2 and you get 40

answer: 31, 5556. 952 seconds

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 =