To divide one power of ten by another, simply subtract the two exponents (see Multiplication/Division). Next, convert the two numbers from scientific notation to real numbers. Now add the two numbers normally. Finally convert to scientific notation if the coefficient is less than 1 or greater than 10.
Precipitation occurs when cloud droplets combine and grow large enough to fall to the earth the rate of evaporation as a drop falls to the earth also can affect its size. from: sadia aisa.
Evaporation: Heat from the Sun causes water on Earth (in oceans, lakes etc) to evaporate (turn from liquid into gas) and rise into the sky. This water vapor collects in the sky in the form of clouds. Condensation: As water vapor in the clouds cools down it becomes water again, this process is called condensation. Precipitation: Water falls from the sky in the form of rain, snow, hail, or sleet, this process is called precipitation. Collection: Oceans and lakes collect water that has fallen. Water evaporates into the sky again and the cycle continues.