9. The diameter of the Earth is 7899.83 miles from the North Pole to the South Pole and 7926.41 miles from opposite points at the equator. a. Find the approximate surface area of Earth using each measure.
b. About 75% of Earth's surface is covered by water. Find the surface area of water on Earth, using the diameter of the Earth is 7926.41 miles from opposite points at the equator.

We could think of the Earth as a sphere, where the diameter of this sphere will the mean diameter between the measure from the North pole to the Soth pole and the measure from opposite points of the equator.

Remember that the mean between two numbers A and B is:

Mean = (A + B)/2

In this case, the mean diameter will be:

D = (7,899.83mi + 7,926.41mi)/2 = 7,913.115 mi

And we know that the surface of a sphere of diameter D is:

S = 4*pi*(D/2)^2

Where pi = 3.14

Then the surface of the Earth will be something like:

S = 4*3.14*(7,913.115mi/2)^2 = 196,618,601.47 mi^2

b) We know that 75% of the Earth's surface is water, now we will use the diameter 7,926.41 mi to compute the surface.

First, the total surface of the Earth will be:

S = 4*3.14*(7,926.41mi/2)^2 = 197,279,843.03 mi^2

And 75% of this is water, then the total water surface is 0.75 times that area, this is:

water surface = 0.75*197,279,843.03 mi^2 = 147,959,882.27 mi^2

step-by-step explanation:

the original amount doesn't ''re just looking for the time it takes for 1/2 of the substance to we have

(1/2) =)     take the ln   of both sides

ln (1/2)   = )   and we can write

ln(1/2) = ) lne     and lne   = 1     so we have

ln(1/2) = -.1092t     divide both sides by -.1092

t = ln(1/2)/-.1092 = about 6.347 days = about 6.3 days (rounded)