How much energy & money do LED lamps save?

Grade level: 4th – 5th grades

Skills: Multiplication

Related environmental issues: Energy conservation

The table below shows how much electricity each light bulb uses to light your room in 1 year.

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  1. Your house has 30 light fixtures.  How much electricity do you use during a year if you use a regular light bulb for each light fixture?
  2. How much electricity do you use during a year if you use an energy saving light bulb for each house’s light fixture?
  3. How much electricity can you save if you replace all of the 30 regular light bulbs with energy saving light bulbs?
  4. The average price of 1kwh-electricity in California was 21 cents in August 2018. How much money could your family save for electricity in a year if you replaced all of the 30 light bulbs with energy saving light bulbs in a year?




Answer keys

  1. 200 x 30 = 6,000 (kWh)
  2. 30 x 30 = 900 (kWh)
  3. 6,000 – 900 = 5,100 (kWh)
  4. 5,100 x 21 = 107,100 (cents) = $ 1,071


How much has the weight of plastic bottles changed?

Grade level: 3rd – 5th grades

Skills: Division 

Related environmental issues: Reduce /  Reuse / Recycle

The average weight of  plastic beverage bottles has changed over time. In 1980, five empty 2-liter PET bottles weighed 340 grams.  Now, nine 3-liter PET bottles weigh 378 grams.


  1. Which weighs more, a plastic bottle in 1980 or now? And how much?
  2. Why do you think has the weight of plastic bottles changed? Explain.

Sources: PET Resin Association, Little-Known Facts about PET Plastic




Answer keys

  1. 1980 bottle: 340 ÷ 5 = 68 (g)   Now: 378 ÷ 9 = 42 (g)    68 – 42 = 22 (g)     A plastic bottle now is 22 g lighter than that in 1980.
  2. Answers may vary: Hint 1) Lightweight plastic bottles reduce the use of plastic and raw materials  2) Lightweight plastic bottles reduce overall weight of the item and reduce energy consumed and CO2 emitted in the process of manufacturing and transporting the item. 3) Lightweight plastic bottles reduce plastic (and raw materials) use, so does the amount of plastic that has to be recycled.