Thread: Can someone help an old man with a math question?

1. Can someone help an old man with a math question?

Sirs,
I have a blueprint with a 40' length drawn at 5.375 (5 3/8").
What scale is that and how long is a foot in that scale.
I don't even know if it is algebra or some other field.
If I knew how to write that as an equation, I could have gotten the
answer on an online calculator. But, since I am practically illiterate in
math, I turn to you.
Thank you
Dan

2. Dan,

Well, what you've got there is a unit conversion problem. You're told that 40' actual = 5.375" drawing. This means that the following is true:

$\frac{40'}{5.375"}=1$, and

$\frac{5.375"}{40'}=1.$

To do a units conversion, you simply multiply by whichever of the correct factors above will cancel the units. You would like to know what 1' is? Well then, you need to cancel the feet in the numerator thus:

$1'\times\frac{5.375"}{40'}=1\times\frac{5.375"}{40 }=0.134375".$

You probably don't have that many significant figures, so you'd probably say something like 1' actual = 0.1343" drawing. Does that make sense?

3. Yes, Sir, it does. Thank you for your time.
How would I calculate what scale that is?
The scale listed on the blueprint is n.t.s.
The results from a Google search tell me that it is either,
"not to scale" which is not the case for a blueprint,
or
National Technical Scale.
I didn't have much luck finding what that means.
Thanks again,
Dan

4. I'm not used to looking at blueprints, so I'm not quite familiar with answering the question, "What scale is that?" I'll try a guess: perhaps you're asking what 1" on the drawing corresponds to in reality? That would be a reverse computation of the previous one. You get

$1"\times\frac{40'}{5.375"}=1\times\frac{40'}{5.375 }\approx 7.442'$.

It would seem strange if a blueprint was not to scale. What use is that? I couldn't find anything on National Technical Scale. I'm not sure I can be of much help with that, I'm afraid.

5. Thank you, Sir.