I am not a epidemiologist. As a EE, my expertise is physics and math. So I am using the facts as put out by CDC and other experts. There are two elements to the spread of virus: exposure and transmission.
Here are some facts:
It takes 15 minutes of exposure in close proximity of an infected person to catch virus with 100% certainity. Half the time cuts the chances to half.
Distance and barriers make transmission harder.Six feet of distance from a sick person reduces the chance of catching virus by 95%. Half the distance quadruples the chances.
Barriers reduce the chances depending on the effectiveness of the barrier. a N95 mask cuts the chances by 95%. An ordinary surgical mask is 80% effective; a home made 3 layer cloth mask is bout 60% effective.
Positivity rate in random testing tells us the chances of running into an infected person; 10% positivity rate ( the current rate in California) says that only one in ten random people we get in contact is likely to be infected.
Given those facts, if we wear a home made mask and come within 3 feet of a stranger who is not wearing a mask and linger for one minute only; our chances of catching virus is is only .0467%, that is less than 1 in 2000. If stranger is also wearing a mask, the chances are reduced further 65% and are now .0163%.If social distance is increased to six feet, chances are further reduced by 75% and are now dow. That is down to .004% or one chance in 25,000.
Given that, if we test and eliminate the infected people, we should be able to open schools and businesses with very little risk.
If positivity rate is 1% as we have in New York now, all we will have to do is make everybody wear a mask and maintain 3 feet distance to open the schools and businesses with little risk.
We live with those kind of risks currently when we drive.