Additional Math Pages & Resources

Tuesday, March 1, 2011

Slyly shifting sizes and prices, Part I

One of the most common requirements of grown-up life is the ability to shift between different units of measure as we buy things. We deal with cents, dimes and dollars, pints and cups, pounds and ounces, kilos and grams. We don't normally do this with spreadsheets and calculators, but in our heads while we are shopping.

Kids learn all about this in our Excel Math curriculum.

While we walk down the aisle of a store frowning over the prices, manufacturers and retailers seem to complicate the process for us. They can adjust both package size and price to get a bit more profit margin for their products without us knowing they've put the price up.

CAUTION: The following content has been chosen simply because there is historical data available. The author and publisher of this website take no responsibility for your actions after reading about chocolate bars, and they do not endorse or prescribe the presence of chocolate bars in the classroom or in the home. Please imagine carrots instead of Hershey bars if it helps your willpower.

Using an innocent example from a company with no obvious motive to dissuade us from buying, here's a list of Hershey bar candy sizes over a 40-year period. The list appears on a nice site called The Food Timeline.

[1946] 1 1/2 oz.....5 cents
[1947] 1 oz.....5 cents
[1954] 7/8 oz.....5 cents
[1955] 1 oz.....5 cents
[1958] 7/8 oz.....5 cents
[1960] 1 oz.....5 cents
[1963] 7/8 oz......5 cents
[1965] 1 oz.....5 cents
[1966] 7/8 oz.....5 cents
[1968] 3/4 oz.....5 cents
[1969] 1 1/2 oz.....10 cents
[1970] 1 3/8 oz.....10 cents
[1973] 1.26 oz......10 cents
[1974] 1.4 oz.....15 cents
[1976] 1.2 oz.....15 cents
[1977] 1.2 oz......20 cents
[1978] 1.2 oz.....25 cents
[1980] 1.05 oz.....25 cents
[1982] 1.45 oz.....30 cents
[1983] 1.45 oz.....35 cents
[1986] 1.45 oz.....40 cents

Notice the constant shifting up and down and the changes in units from fractional to decimal?

Now that you have seen this list, do you have any idea what the cost of a Hershey bar is today, and how many ounces of chocolate are in a "standard" Hershey candy bar?

Me neither. Can we predict from the historical trend? Here's the data in graph form:

A candy bar went from 5 cents to 40 cents in 40 years - how much did it increase in the 25 years from 1986 to 2011? We could do projections, but I just found a current price for a box of candy bars, plotted the final points, and drew dotted lines backwards to show a rough increase rate. Of course, if you just buy one bar at the convenience store or movie theatre, your price could be much higher than this.

Does the math you learned in school help you to be a more informed consumer of chocolate?

I have learned from today's blog that the blue line (candy in stomach) has remained relatively constant while the green line (money handed to cashier) has changed dramatically .

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