Calculating Cable Turns for a Job

[Brian82784]

Hello,

I'm trying to help my kiddo with some math, and unfortunately this is stumping me.

A full reel of cable has a diameter of 60 inches. A job requires 314 feet of cable. How many turns of cable should be taken off the the reel?

The answer is 20 turns, but I can't seem to figure out how to get to that answer.

60 inches = 5ft
60 diameter = 188.5 circumference

 

[berkeman]

Welcome to PF.

Our schoolwork rules require that you show as much work as you can on schoolwork questions. If the wire removed from the spool all has the same diameter, how many circumferences (turns) does it take to add up to 314 feet?

 

[FactChecker]

One hint that I think we can already give is that it looks like the 314 ft is designed to cancel out something. So it might not be good to multiply out the 60*3.14 = 188.4. Let things cancel.

 

[Brian82784]

5 * 3.14 = 15.70
15.70 * 20 =314

 

[berkeman]

5 * 3.14 = 15.70
15.70 * 20 =314

It's good technique to carry units along in your calculations. It helps you avoid mistakes, and helps us understand what you are doing.

 

[Mark44]

60 diameter = 188.5 circumference

The units above are inches -- you are asked to find how many turns to make 314 feet. By happy coincidence, 314 feet is approximately equal to 100$\pi$.

It's good technique to carry units along in your calculations. It helps you avoid mistakes, and helps us understand what you are doing.

+1