Which endangered animal is heavier, Tiger or Leopard?

Grade level: 4th – 5th grades

Skills: Bar graphs

Related environmental issues: Biodiversity

As many as 26,000 species are threatened with extinction in the world because people have changed their habitats, and they lost their homes. The bar graph below shows the weight of some of the most endangered  animals in the world.

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1.Among the endangered animals, which animal weighs the most?

2.Which is heavier, Amur Leopard or Sumatran Orangutan?

3.Which endangered animal weighs twice as much as Hawksbill Sea Turtle?




Answer keys


1.Mountain Gorilla

2.Sumatran Orangutan

3.South China Tiger



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.