I need help with question

Question

The surface of the earth is 70% water. If the diameter of the earth is 8,000 miles, how many square miles of the earth are covered by land.

Answer 1

Hi Jalia,

Here is your question

The surface of the earth is 70% water. If the diameter of the earth is 8,000 miles, how many square miles of the earth are covered by land.

Radius of Earth = 4000 miles ( As Diameter = 8000miles)

Surface area of earth = 4*pi * (Radius) ² = 4*3.14* 4000* 4000 =S ( mile²)

If 70% is water , then remaining land is 30%

So 30 % of Surface are = S' = 0.3 * S = 0.3*4*3.14* 4000* 4000 = Area covered by land ( in mile² ) 30% is 0.3 times

S' = 15072000 mile² =1.51 * 10⁷ square mile

Answer 2

1. You would use the surface area of a sphere for this problem: A = 4(π)r²
2. If the diameter of the earth (given) is 8000 miles, then the radius (r) is 4,000
3. Just plug r = 4000 into the equation for the total earth surface area
4. A = 4(π)r² A = 4(π)4000² = 201,061,929.8 miles²
5. But, the land is only 30% of that (because water covers 70%), so:
6. 0.7(201,061,929.8 miles²) = 140,743,350.9 miles² is land

Does this process make sense to you? I hope! :-)