Tuesday Afternoon (1000+ posts) Thu Aug-18-11 12:34 PM
Original message
If each item on your grocery list goes up by 4% then has the total cost
of your groceries only gone up by 4%?
please show the math.
tia.
The newly unemployed banker Chan790 leaps in with a quick perspicacious answer.
Chan790 (1000+ posts) Thu Aug-18-11 12:45 PM
Response to Original message
1. In MD, no.
Not much math required.
Some items are untaxed as "food" and other items are taxed as "consumables" (the second one being all prepared foods, soda, and a wide definition of junk food that includes things like sweetened breakfast cereal and frozen pizza and jelly but not "preserves" or peanut butter) so the net change in your grocery bill would depend on the quantities of the items purchased and their taxable status.
For example:
2 pizzas @ $8...16 +tax = $17.60
4 bags of taters @ $4 +tax^0 = $16
Same purchase amounts, different totals because of tax-policy.
This answer has one minor drawback...it's utterly wrong, as demonstrated fairly simply:
struggle4progress (1000+ posts) Thu Aug-18-11 07:36 PM
Response to Reply #1
8. That shouldn't matter. Suppose there are n classes of grocery items
C1, C2, C3, ... , Cn
taxed at rates r1, r2, r3, ... , rn
and the prices of all items go up p%
The old total would have been
C1*(1 + r1) + C2*(1 + r2) + ... + Cn*(1 + rn)
The new total is
(1 + p/100)*C1*(1 + r1) + (1 + p/100)*C2*(1 + r2) + ... + (1 + p/100)*Cn*(1 + rn)
= (1 + p/100)*(C1*(1 + r1) + C2*(1 + r2) + ... + Cn*(1 + rn))
So the new total is (1 + p/100) times the old total: the total has gone up by p%. It wouldn't matter if some classes Cj were untaxed (rj = 0)
Clearly not being one to hide his ignorance
Chan790 (1000+ posts) Thu Aug-18-11 10:37 PM
Response to Reply #8
9. This is going to sound very bad because until recently I advised people on major financial decisions
That was entirely over my head, I have about a 5th grade comprehension of mathematics: arithmetic, pre-algebra and I naturally "get" geometry and trigonometry more than my other math skills would suggest. I fulfilled my college math requirements with accounting courses and a visual-math class meant as an elective for engineers and architects. Also, CAD.
If you can diagram that, I might get it.
Major financial decisions...somehow I think not, when simple proportions are beyond you. Wouldn't want him calculating my interest...
The right answer to the original question is even in there:
Lionel Mandrake (1000+ posts) Thu Aug-18-11 05:28 PM
Response to Original message
7. The total goes up by approximately 4%.
The approximation is not exact for two reasons:
1. The price of a single item can not go up by exactly 4% unless that price is a multiple of 25 cents.
2. Taxes are rounded to the nearest penny. Thus it's unlikely that the tax will go up by exactly 4%.
Nevertheless, the total cost increase will be close to 4%
http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=105x9761159I love it when they try to talk clever...
