Scaling : ratio and proportion

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Discussion Overview

The discussion revolves around the application of ratios and proportions in determining the length of a rafter based on a scale provided in a blueprint. Participants explore the conversion of measurements and the implications of the scale in both inches and feet.

Discussion Character

  • Homework-related
  • Mathematical reasoning

Main Points Raised

  • One participant presents a scale of 1/8" = 3' and asks for help in calculating the length of a rafter measuring 1 3/8" on the blueprint.
  • Another participant suggests converting the measures to the same units, proposing a scale of 1:288 after multiplying through by 8.
  • Questions arise regarding the calculations of 36 and 288, with clarifications provided that 3 ft. equals 36 in. and the multiplication leads to 288.
  • One participant expresses understanding of the initial conversion but seeks guidance on breaking down 1 3/8" and solving for the corresponding values.
  • Another participant suggests expressing 1 3/8" as an improper fraction (11/8) and multiplying by 288 to find the actual length.
  • One participant calculates 11/8 as 1.375 and multiplies by 288 to arrive at 396, questioning whether to convert this to inches.
  • A subsequent reply confirms that 396 represents inches and suggests converting to feet, while also reinforcing the relationship between the scale and the calculated length.

Areas of Agreement / Disagreement

Participants generally agree on the method of converting measurements and the calculations involved, but there are questions and clarifications regarding specific steps and interpretations of the results.

Contextual Notes

There are unresolved aspects regarding the clarity of the conversion process and the interpretation of the final results, particularly in terms of unit conversions.

Eabzolid
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Hey guys.
Last question I have is

A scale on a drawing is 1/8" = 3'. Determine the length of a rafter if it measures 1 3/8" on the blueprint.

Thanks
 
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First, convert both measures to the same units...let's use inches to get a scale of:

$$\frac{1}{8}:36$$

Multiply through by 8:

$$1:288$$

This means a length of one unit on the blueprint represents 288 of the same unit in the actual building. Can you proceed? Can you find a shortcut rather than use the more general procedure I gave?
 
How did you get those numbers? 36? And 288?
 
Eabzolid said:
How did you get those numbers? 36? And 288?

3 ft. is 36 in., and then when multiplying by 8 we get 288. :D
 
Okay. I get the first part.

How do I break down the 1 3/8"? And then solve for both values?
 
Eabzolid said:
Okay. I get the first part.

How do I break down the 1 3/8"? And then solve for both values?

I would express it as an improper fraction...that is:

$$\frac{11}{8}$$

Then multiply by 288. Or, you can use the following reasoning:

If 1/8" represents 3' then what must 11/8" represent?
 
I put 11/8= 1.375
1.375x288=396

Do I then convert 396 to inches?
 
Eabzolid said:
I put 11/8= 1.375
1.375x288=396

Do I then convert 396 to inches?

That number represents inches...you should convert to feet.

What I was trying to get at before is that if 1/8" equals 3', then 11 times 1/8" must represent 11 times 3' or 33' (which is 396 inches). :D
 

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