%error=(6.5g/mol - 7g/mol)/(7g/mol) * 100= 7.14% error
Answer:
Speed of boat in still water is 6km/h
Speed of current is 4km/h
Step-by-step explanation:
We know speed = distance / time
Let the speed of boat in still water be x
Let the speed of current be y
Hence the speed of boat, down stream = 
Distance downstream = 20km
Time taken = 2 hours
We have

......(1)
Speed of boat upstream = 
Distance upstream = 4
Time taken = 2
We have

...(2)
Adding (1) & (2)


Substituting in (1) we get

Answer is 12.50. u can comment on my answer if you would like to see how that is the correct answer :)
12/$3=20/x is the formula. Then cross multiply to get 12x=60, so x=$5.
1.75 would be the direct center between those two irrational numbers.