



 
Shelly, The first thing I do is make an estimate so that when I do the problem precisely I know approximately what to expect.
To get from "2 inches represents 25 feet" to "1 inch represents 12.5 feet" I divided both numbers by 2. What if I divide both numbers by 25?
I hope this helps,
Hi Shelly. A scale can be thought of as a fraction. So for the scale 2 inches: 25 feet, that is the fraction 2/25. When "building to scale" you want to use the same ratio for all the parts. Therefore, the question is asking you for an equivalent fraction with ?/60. Let me show you how to solve it using a different number. Let's say the engine is 20 feet long. So I will try to find the equivalent fraction for ?/20. To transform fractions from one denominator to a different denominator, you just have to remember that whatever you do to the bottom, you must do to the top. So I divide 20 by 25 and I get 0.8. That means that by multiplying the 25 by 0.8, I get 20. So to see what the 2 becomes, I have to multiply it by 0.8 as well. 2 x 0.8 = 1.6. So the model engine needs to be 1.6 inches long. Now you try it for a 60 foot length. Stephen La Rocque.  


Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences. 