October 3rd, 2016, 02:29 AM  #21 
Senior Member Joined: Apr 2014 From: Glasgow Posts: 2,049 Thanks: 680 Math Focus: Physics, mathematical modelling, numerical and computational solutions  
October 3rd, 2016, 06:07 AM  #22 
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 10,477 Thanks: 693 
Attaboy, Big Ben 
October 3rd, 2016, 06:11 AM  #23 
Newbie Joined: Sep 2016 From: USA Posts: 14 Thanks: 3 
@v8archie What exactly do you mean by my route? 
October 3rd, 2016, 06:14 AM  #24 
Math Team Joined: Dec 2013 From: Colombia Posts: 6,940 Thanks: 2267 Math Focus: Mainly analysis and algebra 
Your solution.

October 3rd, 2016, 08:41 AM  #25 
Newbie Joined: Sep 2016 From: USA Posts: 14 Thanks: 3 
Ah so to clarify you were talking about the steps I suggested trying. (Which I said I understood wasn't the best solution for the OP, because I forgot for a moment what you meant by the sum of 1/x + 1/y) As opposed to finding the approximate the range of correct answers by plugging in some values and seeing if what values are close to solution so you'll know what techniques to possibly use (if you don't know what to do at the start of a problem). This was in another thread but I thought you were referring to it, since I didn't really provide a route to the OP in dealing with problems in general as opposed to showing him a way to think about this problem and what steps he could do based on that way of seeing it. And I would think that would be an unlikely thing you'd mean as my route since I also admitted I overestimated the problem. I just want to be completely clear on what you were saying. Last edited by skipjack; December 1st, 2016 at 03:05 PM. 
October 3rd, 2016, 09:34 AM  #26 
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 10,477 Thanks: 693  
November 1st, 2016, 05:44 PM  #27 
Senior Member Joined: Jan 2014 From: The backwoods of Northern Ontario Posts: 371 Thanks: 68 
V8Archie, do you mean? $\displaystyle \frac{1}{x} + \frac{1}{y}$= $\displaystyle \frac{y}{xy} + \frac{x}{xy}$= $\displaystyle \frac{x+y}{xy}$= $\displaystyle \frac{4}{5}$ 
November 4th, 2016, 02:47 AM  #28 
Newbie Joined: Jun 2016 From: india Posts: 24 Thanks: 4 
1/x + 1/y Take L.C.M =(x +y)/xy ....(1) It is given that , x+y = 4 and xy = 5 Put these values in eqation (1) = 4/5 
November 4th, 2016, 04:12 AM  #29 
Global Moderator Joined: Oct 2008 From: London, Ontario, Canada  The Forest City Posts: 7,576 Thanks: 931 Math Focus: Elementary mathematics and beyond 
1/x + 1/y = z x + y = xyz 4 = 5z z = 4/5 
November 9th, 2016, 01:51 AM  #30 
Newbie Joined: Jun 2016 From: india Posts: 24 Thanks: 4 
(1/x) + (1/y) = (x+y)/(xy) Put x+y = 4, xy = 5 = 4/5 This is the required answer. 

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