Question

if 1 gallon of paint covers 400 square feet, about how many gallons of paint are needed to paint the outside of a spherical tank diameter 20 feet

Answer 1

Given:
Diameter if the spherical tank = 20 ft.
Now,
We know,
radius = diameter / 2
= 20 / 2
= 10 ft.
Now,
The area of the spherical tank =
`4 \pi r^(2)`

=
`4 \pi (10)^(2)`

=
`4 * \pi *100`

=
`1256.637061`

=
`1256.64~ft^2-->rounded`

Now,
According to the question,
400 ft² needs 1 gallon of paint
1 ft² needs (1 / 400) gallon of paint
1256.64 ft² needs (1 / 400) * 1256.64 gallon of paint
= 3.1416 gallon of paint
= 3.14 gallon of paint --------------> rounded

So, we need 3.14 gallon of paint