Additional Math Pages & Resources

Tuesday, July 27, 2010

Coins in the ashtray

Foolish me. I left my wallet in my desk drawer went I went to lunch, and had to use change from my car's ashtray to buy some food. Time to use my elementary math education, right?

Later I found a site today that promised to calculate the value of coins in a jar. Or in my case, the ashtray. I put all my remaining coins in a container, weighed the total amount, dumped out the coins, weighed the container, subtracted it from the total, and came up with:

1.10 pounds of coins in the ashtray

Then following the instructions, I grabbed a small handful of coins.
I counted out how many of each kind of coin:

7 pennies
5 nickels
5 dimes
3 quarters
20 total coins in the handful I grabbed.

According to the website, that equals a total of:

0.038581 pounds of pennies.
0.055115 pounds of nickels.
0.025000 pounds of dimes.
0.037500 pounds of quarters.

0.16 pounds calculated weight of handful
7.04 total handfuls in ashtray (estimated)
$1.57 value of my handful
$11.06 total estimated value of my coins

Actually I had $12.30 cents left, after the $2.18 I spent on food for lunch. So the calculator was inaccurate or my small handful was not a representative sample of the coins.

How does it work? They take the weight of the number of coins in the handful (assuming it's a normal distribution of coins to match the rest in the jar), they calculate the possible coins of each weight, then guess-timate a total.

Counting manually works just fine for me, because it took only about 2 minutes to sort the coins and count up my $12.30 - less than it took to do the coin counter web tool.

But if you have gazillions of coins, you need a coin counting machine. For some unexplained reason, we have 11 in our warehouse. Call if you want to buy one!

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