Question 29116
If they vary inversely p=k/s where "k" has to be determined.
If price =18.5 when s=4000000 then 19.5=k/4000000 and k=78000000
So your equation is p=78000000/s
If te amount of oil is decreases by 3000000 the supply will 
be 1000000 and s=78000000/1000000=$78
Cheers,
Stan H.