Question 929784
You need to find the surface area of the tank (if the shell is thin enough, then the outside & inside surface areas are roughly the same)



We will use the formula SA = 2pi*r^2 + 2*pi*r*h, where,



SA = surface area
r = radius
h = height



In this case,



r = 7/2 (cut the diameter in half)
h = 5



SA = 2pi*r^2 + 2*pi*r*h


SA = 2pi*(7/2)^2 + 2*pi*(7/2)*5


SA = (119/2)*pi


SA = 186.924762888592 (this is approximate)



The surface area of the inner walls of the tank is approximately 186.924762888592 square feet.



We are told that "One gallon of corrosion preventative will cover 10 ft^2"



so we have this ratio: (1 gallon/10 ft^2)



and we use this to determine how many gallons we'll need



Multiply the surface area by the ratio shown above



(186.924762888592 ft^2) * (1 gallon/10 ft^2) = 186.924762888592/10 = 18.6924762888592


Round up to the nearest whole gallon to get 19



You will need <font size=5 color="red">19 gallons</font> of the corrosion preventative. You'll have leftover amount of corrosion preventative, but at least you won't come up short (as compared to getting 18 gallons).

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