Answer:
3500
Explanation:
Number of germs that a scientist can see under a microscope = 1000 germs
We need to find how many germs will there be in 7 hours if the germs double in number every 4 hours .
It's given that the germs double in number every 4 hours .
So, increase in number of germs in one hour = 
 
 
Increase in number of germs in seven hours = 
 
 
Therefore , number of germs in 7 hours = Increase in number of germs in seven hours × Number of germs initially 
= 

So, number of germs in 7 hours if the germs double in number every 4 hours = 3500