The Department of Mathematics and Science Education

tiffani c. knight

I chose to use the Stamps data to generate a prediction from the data given from the spreadsheet.

year	rate(in cents)
1919	2
1932	3
1958	4
1963	5
1968	6
1971	8
1974	10
1975	13
1978	15
1981	20
1985	22
1988	25
1991	29
1994	32
1997	33
1999	34
2002	37

2006 39

As you can see, we were given data on the price of stamps from 1919 until 2002. It’s 2006 now and stamps cost 39 cents, so that’s some information we can add. Alright, let’s see if I can see a pattern…it increased 1 cent in thirteen years, then 1 cent in twenty six years, then 1 cent in five years, then 1 cent in another 5 years, 2 cents in three years, another 2 cents in three more years, 3 cents in one year, 2 cents in three years, 5 cents in three years, 2 cents in four years, 3 cents in three years, 4 cents in three years, 3 cents in 3 years, 1 cent in three years, 1 cent in two years, 3 cents in 3 years, and finally, 1 cent in the last 4 years.

That just looks like a whole lotta words to me. Stamps were only 2 cents back in 1919! I had no clued. Let’s see, they cost 15 cents when I was born and ten cents more when my younger sister was born…guesses as to what year she was born?

Okay, lets get a graph…these words are too much. And I am such a visual person. I used excel to create this masterpiece:

Well, from this graph alone, it’s easy to see that the cost of stamps rise as the years go on and that is due to a lot of different things, I’m sure…but I won’t get into those possible reasons.

Now, I’ve graphed the relationship of an observation, now I have to generate a function and make a prediction as to when the cost of a first class postage stamp will reach a buck ($1.00), $0.64, and when the next 3 cent increase can be expected.

Okay, I was told that I needed to add a trendline and a function. I had no idea how to do this because I’ve never done it before. So I went to the help option on Microsoft and searched how to add a trendline. The directions were easy to follow, and I think I did it correctly, this is what I got:

It looked fine to me, so I moved on to trying to add a function…and that wasn’t so easy. I read and read, but it didn’t help much. So, I followed the instructions as best I could. I filled in a few years and then used the fill thingy to create a few more years in my data. Then I selected all of the data from the cost per stamp, and used the right mouse button to fill in costs. This is my result:

year	rate(in cents)
1919	2
1932	3
1958	4
1963	5
1968	6
1971	8
1974	10
1975	13
1978	15
1981	20
1985	22
1988	25
1991	29
1994	32
1997	33
1999	34
2002	37
2006	39
2007	41.51633987
2008	43.91572067
2009	46.31510148
2010	48.71448228
2011	51.11386309
2012	53.51324389
2013	55.9126247
2014	58.3120055
2015	60.71138631
2016	63.11076711
2017	65.51014792
2018	67.90952872
2019	70.30890953
2020	72.70829033
2021	75.10767114
2022	77.50705194
2023	79.90643275
2024	82.30581355
2025	84.70519436
2026	87.10457516
2027	89.50395597
2028	91.90333677
2029	94.30271758
2030	96.70209838
2031	99.10147919
2032	101.50086
2033	103.9002408
2034	106.2996216
2035	108.6990024
2036	111.0983832
2037	113.497764

Now, I guess I’m ready to answer the questions. From my data, the cost of a stamp will reach a buck in about the year 2032 and 64 cents in about the year 2017. Finally, we can expect to see the next 3 cent increase in the year 2010.