The cafeteria at work has a fairly decent salad bar. The cost is $0.28 per ounce. When you pay for it, they weigh it on a scale that registers the weight in pounds, to three decimal points.
So what's the point? Well, I like salads. And, more importantly, if you can guess the price of your salad—to the penny—then it's free. You are allowed to see the weight (in pounds) and know the price (per ounce) and are even given a moment to do some mental calculations (though I suspect calculators would be prohibited).
I suspect what makes it difficult for most people, even knowing the price and the weight, is remembering that there are sixteen ounces in a pound, and calculating accordingly. It would be a lot simpler if the pricing and the scale were in metric units.
But we can probably compensate just by calculating what 1/10th of a pound of salad costs, and practicing multiplying by that unit.
$0.28 per oz, with 16 ozs. per lb. means a salad costs $0.28 x 16 = $4.48. Each tenth of a pound costs $0.448 (hundredth is $0.0448 and thousandeth is $0.00448).
| Weight | Price | Weight | Price | ||
|---|---|---|---|---|---|
| 0.10 lbs. | = | $0.448 | 0.55 lbs. | = | $2.464 |
| 0.15 lbs. | = | $0.672 | 0.60 lbs. | = | $2.688 |
| 0.20 lbs. | = | $0.896 | 0.65 lbs. | = | $2.912 |
| 0.25 lbs. | = | $1.120 | 0.70 lbs. | = | $3.136 |
| 0.30 lbs. | = | $1.344 | 0.75 lbs. | = | $3.360 |
| 0.35 lbs. | = | $1.568 | 0.80 lbs. | = | $3.584 |
| 0.40 lbs. | = | $1.792 | 0.85 lbs. | = | $3.808 |
| 0.45 lbs. | = | $2.016 | 0.90 lbs. | = | $4.032 |
| 0.50 lbs. | = | $2.240 | 0.95 lbs. | = | $4.256 |
I've personally only ever seen their scale register a zero or a five in the third decimal place. If it's a zero, nothing needs to be added to the overall price. If it's a five, then $0.022 needs to be added to the total.
I've included beyond two decimal places on the dollar amounts above because if you round prematurely you might end up being off by a penny—and if that happens, the lunch won't be free...
—Michael A. Cleverly
Tuesday, March 29, 2005 at 23:29