My Math Forum Hard Fraction problem

 Elementary Math Fractions, Percentages, Word Problems, Equations, Inequations, Factorization, Expansion

October 3rd, 2016, 02:29 AM   #21
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Quote:
 Originally Posted by Denis Greg, I was trying to "lengthen" this useless thread
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 October 3rd, 2016, 06:07 AM #22 Math Team   Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 9,051 Thanks: 621 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: 6,687 Thanks: 2175 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 04:05 PM.
October 3rd, 2016, 09:34 AM   #26
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Page#3, post#26 a'comin up!

Quote:
 Originally Posted by IamHere If x + y = 4 and xy = 5, then 1/x + 1/y = ?
xy = 5 is not required, except for wrapup.

x + y = 4
1/x + 1/y = (x + y) / (xy) = 4/5 : over and out.

Take x=7 and y = 4:
1/x + 1/y = 1/7 + 1/4 = (4 + 7) / (7 * 4) = 11/28 = (x + y) / (xy)

 November 1st, 2016, 05:44 PM #27 Senior Member   Joined: Jan 2014 From: The backwoods of Northern Ontario Posts: 367 Thanks: 68 V8Archie, do you mean? $\displaystyle \frac{1}{x} + \frac{1}{y}$= $\displaystyle \frac{y}{xy} + \frac{x}{xy}$= $\displaystyle \frac{x+y}{xy}$= $\displaystyle \frac{4}{5}$ Thanks from jonah and v8archie
 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: 7,473 Thanks: 884 Math Focus: Elementary mathematics and beyond 1/x + 1/y = z x + y = xyz 4 = 5z z = 4/5
 November 9th, 2016, 02:51 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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