This Week From Bedtime Math: Rubber Band Man

It might be a stretch to get every color of the rainbow into one bracelet, but give it a shot anyway in today&s challenge from Bedtime Math!
By Laura Overdeck
Mar 25, 2014



Mar 25, 2014

What is Bedtime Math? A message from Laura: Bedtime Math is a pretty simple idea: We all know we should read to our kids at night, but what about math? My husband and I have done fun, mischief-loaded math problems with our kids at night for years, and when at age 2 our third child started hollering for his own math problem, we realized we were onto something:  In a world where so many people say, "Ewww, math!" we had created a household culture where kids don't just tolerate math, they actually seek it out. Now, every week, we'll be posting a new problem right here on Scholastic Parents!
You may have heard of Rainbow Loom, the awesome toy that lets kids loop colorful rubber bands onto pegs, then pull them off in a chain to make bracelets, rings, even pocketbooks. The math behind those designs is cool, but so are the numbers behind the business. Cheong-Choon Ng invented the loom for his daughters so they could make friendship bracelets more easily. All their friends loved it, so Ng and his wife took all their money– about $10,000 – and spent it making a batch of looms and rubber bands that they could sell. But there were problems. The first rubber bands showed up covered in dust, so the Ng family had to wash them all in the bathtub and hang them on racks to dry. Then the first hooks were made the wrong size, so Ng had to file each one down to shorten them – it took him a whole year. Of course, he's now sold over 3 million looms, and at $15 each it's clear that the hard work is paying off.

Now that we've "hooked" your interest, try challenging your kids to these math problems:

Wee ones: If a Rainbow Loom kit needs 1 loom, 2 bags of rubber bands, 1 hook, and the box to hold it all, how many parts in total get put together?

Little kids: If it costs 4 cents to make a rubber band but you can sell it for 7 cents, how much extra money ("profit") do you make on each rubber band?  Bonus: What would you make on 10 rubber bands?

Big kids: If it costs Ng $10 to pack a Rainbow Loom kit that he then sells for $15, how much profit (leftover money to keep) has he made on the 3 million kits?  Bonus: If he spent another $9 million on factory space, storage space, and so on, now how much profit did he make – and how much profit on each of the 3 million kits?
Wee ones: 5 parts.
Little kids: 3 cents on each.  Bonus: 30 cents.
Big kids: $15 million, since he keeps an extra $5 on each.  Bonus: He's now made just $6 million in profit, which comes to $2 per kit for 3 million kits. Those chunky costs are called "overhead" and the more kits he sells, the more he spreads out those costs and the less extra cost on each kit.

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