What is the weight of the apple?

3/12/2010

I knew that 2nd graders study fractions this month, so I decided to give them 'fraction' problem.

The weight of the apple is 400 grams. What is the weight of 1/5, 3/10, 3/4 of that apple?

To determine the weight of 1/5, kids drew an apple and divided it into 5 parts. However it proved to be a very complicated task for them.

Then we started with more simple problem. Let's say the weight is not 400, but 100 grams. What is the weight of 1/2? Kids replied: 50 grams. Correct! What is the weight of 1/4? 25 grams, kids replied. Correct! What is the weight of 3/4? 75. Correct!

Now back to the original problem, the weight is 400 grams. What is the weight of 1/2? 200 grams. Correct! What is the weight of 1/4? 100 grams. Correct! What is the weight of 1/5? This was still difficult for kids.

I drew a circle representing an apple. Divided circle with 5 equal parts. Each part is 1/5. I marked each part with ?. We have ? + ? + ? + ? + ? = 400 grams => 5 x ? = 400 grams. What number do you need to take 5 times to get 400? Kids replied: 80. Correct! What is 2/5 then? Kids replied: 160. Correct! What is 3/5? 240. Correct!