Question

a model of earths water budget shows that the precipitation on oceans is 420,000 km³ and the precipitation on land is 130,000 km³. if the evaporation from land is 90,000 km³, how much is the evaporation from oceans?
90,000 km³
130,000 km³
460,000 km³
550,000 km³

Explanation:

Step1: Recall water - budget principle

The total precipitation on Earth must equal the total evaporation on Earth. Let the evaporation from oceans be $x$. The total precipitation is the sum of precipitation on oceans and land, and the total evaporation is the sum of evaporation from oceans and land.
Total precipitation = $420000 + 130000=550000$ $km^{3}$
Total evaporation = $x + 90000$ $km^{3}$

Step2: Set up equation and solve

Since total precipitation = total evaporation, we have the equation $x+90000 = 550000$.
Subtract 90000 from both sides of the equation: $x=550000 - 90000$.
$x = 460000$ $km^{3}$

Answer:

C. $460,000\ km^{3}$