You never know what’s buried right under your feet. Well, one California couple found real treasure in their backyard! When they saw a can sticking out of the ground, they dug and dug, and found eight cans filled with 1,427 gold coins! The mix of $5 coins, $10 coins and $20 coins was minted (made) between 1847 and 1894, back when Americans used coins for those amounts. If you add up all those $10s and $20s, the coins have a total face value of almost $28,000. But they’re worth far more than that, because the older a coin, the fewer of that coin we still have, and so the more people will pay to own that coin. One of the coins is worth over $1 million all by itself, and all together the collection could sell for about $10 million!

*Wee ones:* Which has a bigger number on it, a $5 coin or a $10 coin?

*Little kids:* If you found two $5 coins, how much money would you have? *Bonus:* If the coins are worth $10 million total and just 1 of them is worth $1 million, how much are the others worth all together?

*Big kids:* If you pulled out a $5 coin, then a $10, then a $20, then a $5 again to repeat the pattern…how much would the first 6 coins be worth together? *Bonus:* If the couple buried the 1,427 coins again in bags, with at most 100 coins in each, at least how many bags would they need?

*The sky’s the limit:* If there were equal numbers of $20s, $10s and $5s, how many of each would you need for the face value to add exactly to $28,000?

Answers:

*Wee ones:* The $10 coin.

*Little kids:* $10. *Bonus:* $9 million.

*Big kids:* $70. *Bonus:* At least 15 bags, since 14 bags would hold only 1,400 coins.

*The sky’s the limit:* One trio of a $20 coin, a $10 and a $5 adds up to $35, so you just need to find out how many sets of $35 go into $28,000 — and you can guess it will go evenly, since both are divisible by 7! 8 sets of $35 are worth $280, and you need 100 times as much as that, so you need 800 of each coin.

Laura Bilodeau Overdeck is founder and president of Bedtime Math Foundation. Her goal is to make math as playful for kids as it was for her when she was a child. Her mom had Laura baking before she could walk, and her dad had her using power tools at a very unsafe age, measuring lengths, widths and angles in the process. Armed with this early love of numbers, Laura went on to get a BA in astrophysics from Princeton University, and an MBA from the Wharton School of Business; she continues to star-gaze today. Laura’s other interests include her three lively children, chocolate, extreme vehicles, and Lego Mindstorms.