Answer:
80,000
Step-by-step explanation:
First, the diameters of both must be in the same unit. Converting the pinhead diameter from millimeter to nanometer, we get:
nm
To get the number of polio viruses that fit at the head of the pin, divide the pin size by the amount of virus in nanometers:
![2*10^6 = 2,000,000](https://img.qammunity.org/2019/formulas/chemistry/middle-school/dby7eox8kxue43s09ry73j8nj582j97yle.png)
![2,000,000 / 25 = 80,000](https://img.qammunity.org/2019/formulas/chemistry/middle-school/ro1kqgn7jgd4sfk7sx7kj7dww2tbhyte79.png)
This concludes that 80,000 polio viruses fit the pinhead.