Americans combined drive about 4.0×109 miles per day and their vehicles get an average of 20 miles per gallon of fuel used. For each 1 kg of gasoline that is burned, about 3.0 kg of CO2 are produced. How many kilograms of CO2 are emitted into the atmosphere each day by cars in the U.S.? One gallon of gas weighs about 3.5 kg.

Question

My answer is 2.1x10^8, is this correct?

Answer 1

I don't think so but let's see.
4E9 miles/day x 1 gallon/20 miles = 2e8 gallons gasoline/day burned.
2e8 gallons gasoline x 3.5 kg/gallon = 7e8 kg gasoline
For every kg gasoline you get 3.0 kg CO2 so
7e8 kg gasoline x 3.0 kg CO2/1 kg gasoline = 2.1e9
Check my work to make sure I didn't make a decimal error.

Answer 2

Ohh, i guess i miscount the 0 when moving the decimal. thank you :)