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Bad Math
Dirty
mudcub
Quiz time: I was trying to read a building schematic yesterday, and there was an interior wall that was 7 3/8 inches long on the blueprint. In the upper-right corner of the page, it said 1/4" to 1'.

Question: how long is the wall in real life?

Answer: scroll down to see. Or, give the answer in the comments, along with an explanation of how you got it

The teacher gave out a one-page sheet "explaining" how to do the problem. Here is the entire method he wanted us to use (copied verbatim)

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Calculation 1
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This calculation deals with the whole number measurement. In this example, the whole number is 7.

The formula is
4 feet x ____ = ____

Therefore, the calculation is
4 feet x 7 = 28

Calculation 2
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Before presenting the calculation, here are some charts that the calculation will use:

Partial Measurement Translation
If the measurement equals Then the Actual Footage equals
1/2 inch = 24 inches or 2 feet
1/4 inch = 12 inches or 1 foot
1/8 inches = 6 inches or 1/2 foot
1/16 inches = 3 inches or 1/4 foot

Handy Guide
If the calculation result is Then the Actual Footage equals
12 inches = 1 foot
24 inches = 2 feet
36 inches = 3 feet

The formula is
1. Check the measurement for the partial number. In this example, the number is 3/8.
2. Check the Partial Measurement Translation for the amount that the bottom part of the fraction matches (denominator). In this example, the number is 8 and the chart says that 8 equals 6 inches.
3. Check the partial number for the top part of the fraction (numerator), In this example, the number is 3.
4. Multiply 6 (the chart translation for the bottom part of the fraction) by the top part of the fraction which is 3. The answer to 6 x 3 is 18 inches.
5. Check the Handy Guide. 18 inches is bigger than 12 inches but smaller than 24 inches. Therefore, the measurement equals 1 foot 6 inches or 1 1/2 feet (18-12 = 6 inches and the 12 inches = 1 foot)
6. Here is the calculation in numerical format:
a. Bolded Step 2 x Bolded Step 3 = Step 4. (6 x 3 = 18)
b. Handy Guide Smaller Number - Step 4 = A complete foot/feet measurement and a remainder.

Calculation 3
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This calculation provides the final answer.

The formula is
Result of Calculation 1 + Whole Number Result of Calculation 2 + Remainder Result of Calculation 2

28+1+6 or 29 feet and 6 inches or it may be expressed as 29 and 1/2 feet.

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Rant: Are you kidding me?!?!?! Are you FRICKING KIDDING me? This is the way they teach kids to do math? I hope you realized that the whole problem is just multiplying 7 3/8 by 4.

Now, I understand that a lot of high school graduates may not be good at math and don't understand fractions. But judging from the above, I can understand how someone could develop a huge FEAR of mathematics. It definitely doesn't promote understanding the calculation. The instructor's answer took seven steps and TWO LOOK-UP TABLES! There is no reason that this problem should require two look-up tables.

It turns out talking to some construction workers that some guys keep a cheat sheet with their tools listing the most common wall lengths and how long they would be on a blueprint. Or, if something is 7 3/8", they just cut the wood at 28' and add "a little extra". But I can imagine with a foreman yelling at you and knowing any mistake could cost the company lots of money, the measurements could get really screwed up.

Maybe we should all try to go metric and then give everyone calculators.

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(Deleted comment)
I would say that that this is a route for people to learn to do these calculations in their head, rather than on paper. It's going into exquisite detail about it, but it isn't describing anything that isn't actually happening along the way. For some people that really have to work for it, this is maybe a good way for them to learn.

In my own words, I would say it more briefly: 7x4 = 28, then 3/8 x 4 = 12/8 = 1.5. So, 29.5 feet.

(Deleted comment)
John is in a bedroom loft and wants to piss in his pants; he does so. But the piss dribbles down warm, wet butt, soaks into his jeans, and eventually dribbles from the loft, wetting his $542 Stereo and his $614 computer. Smoke appeared.

Q: How much did it cost John to piss in his pants?

I got the 28' part, but scrolled down to read your post rather than multiply 3/8 x4


7 3/8" = 7.375"

convert from 1/4"s to ft

7.385" * 1 ft/.25" = 29.54 ft

29' 6.48"


And this is where we all break into the chorus from Tom Lehrer's "New Math".


New Math!
New-ew-ew Math!
It won't do you a bit of good to re-learn math.
It's so simple.
So very simple.
That only a child can do it!

This is NOT how a math teacher teaches kids to do math.

This might be how a shop teacher provides a way for the kids who can't work with fractions to get the correct answer, because he doesn't have the time to teach them how to work with fractions.

You said "he wants us to use" -- what kind of class is this? What's the educational background of other people in the class?

---

True story:

In my Economics 101 class in college, the professor told us to find the middle number in a range, you add the numbers on the edge of the range and divide by two. Some genius in the 250 person lecture hall raised his hand and asked, "does that mean you take the average of the two numbers?" The prof replied, "Hell, I don't know, just add the numbers and divide by two!"

I was appalled by both of them.

***Happy Birthday***


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