20 million people across the U.S. were estimated to have participated in the first Earth Day. More than a billion people in 180 countries around the world now celebrate Earth Day every year.  What is the percentage increase from 20 million to 1 billion?

Here are some more Earth Day math problems:

1. Making new cans from used aluminum cans uses 75 percent less energy than making a can from new materials. It takes 200 million Btu’s (British Thermal Units) to produce a ton of aluminum cans from new materials and only 50 Btu’s to produce a ton of aluminum cans from used cans. How many Btu’s are needed to make 3 tons of aluminum cans from used cans? How many cans can be made with 75 Btu’s?
2. In 1997, the U.S. recycled 13 million cars, which conserved 32.5 billion pounds of iron ore, 18.2 billion pounds of coal and 1.5 billion pounds of limestone.  If in 2015 we recycle 18 million cars how much iron ore will be conserved?  How much coal will be conserved?
3. Recycling 1 aluminum can saves enough energy to run a TV for 3 hours.  If your TV runs 84 hours this month how many aluminum cans should you recycle to produce the energy needed?
4. A leaky faucet can waste up to 20 gallons of water per day, and a leaking toilet can waste up to 200 gallons a day.  If 3 leaky faucets and 2 leaking toilets were fixed now how many gallons of water would be saved each day?