Tek-Tips is the largest IT community on the Internet today!

Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!

  • Congratulations TugboatEng on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Math question - weighted average 1

Status
Not open for further replies.

sabrepoint

Electrical
Joined
May 1, 2003
Messages
30
Location
NZ
Hi All

Not really electrical engineering, but I'm trying to apply formula to engineering problem ...

The following formula determines the Weighted Average Life (Lavg) of a group of power poles ...

Lavg = Qconc/Qtot * 60 + (Qtot-Qconc)/Qtot * 45

where Qconc is quantity of concrete poles, Qtot is the total of all poles (ie: concrete and wooden), 60 is the standard life of concrete poles and 45 the standard life of the remaining (wood) poles. All OK so far if we know the pole quantities.

My problem is going backwards ie: I know Lavg and Qtot but need to determine Qconc. So the question is, how to rearrange to formula to give Qconc?

Your help is most appreciated.
Graeme
 
Qconc=Lavg/(60/Qtot-45/Qtot)+45)

Margin of error %90

 
Hi sabrepoint

I took the numbers 60 and 45 to be multiplying the whole of their respective adjacent ratio's and therefore get an expression:-


((Lavg - 45)* Qtot)/15 = Qconc



regards desertfox
 
Status
Not open for further replies.

Part and Inventory Search

Sponsor

Back
Top