GRADE  4 - 6 / Age 9-11

Weighing in at 300 lbs...

The ability to weigh things is very important in business. Many items are bought and sold according to weight. Many food items are sold by weight.

1) For example, breakfast cereal usually comes in a box with the weight listed on the box. Sometimes, when you open the box, it does not seem full to the top. Do you think you have been cheated? Can you explain why the box is not full but there is still the correct weight of cereal? Is weight a good way to sell cereal? Is there a better way?

2) We all know how important it is to consider recycling. When paper and cardboard are recycled, the recycler weighs the paper in an unusual manner. Large amounts of paper is very heavy and is usually brought in to recycling plants in trucks. First, the truck with the paper loaded on the truck is driven onto a large scale and the weight of the truck and paper is written down. Second, the paper is dumped out of the truck and then the truck is weighed again without the paper and this weight is written down. Finally, using these two measures, the weight of the paper to be recycled can be calculated. Explain how this is done. Make up an example with possible weights.

3) Although size is a consideration, the post office charges you to mail items based on the weight of an item. Why is weight used instead of size?

Sometimes, when you mail lots and lots of the same item, if you pay a fee you can get a bulk rate--a special rate because you send so much mail. When you send mail by bulk, the postal clerk takes a random sample from all the items of mail, say 10 items or so, and then weighs all of them together. The clerk uses this weight to find how much each item weighs. What is a random sample? How does the clerk do this? What does the clerk do to find the weight of one piece of mail based on the sample? Can you think why the clerk doesn't just weigh one item?

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