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 Help Me With A Very Easy Math Problem
 Zweed From Netherlands, joined Apr 2004, 455 posts, RR: 0Posted Sun Jun 5 2005 14:39:52 UTC (10 years 11 months 4 days 19 hours ago) and read 2735 times:

 It's sunday afternoon and my girlfriend is taking some math classes, she asked for my help and as I said, its sunday afternoon and I my total lack of math skills is even larger than they would be without this hang over, A parking lot has the area of 900 sq. metres, it has be rectangular A fence is going to be built around this lot. What dimension will give us the least amount of money spent on the fence? Thanks
 12 replies: All unread, jump to last
 Wunala From Australia, joined Mar 2005, 951 posts, RR: 0 Reply 1, posted Sun Jun 5 2005 15:04:39 UTC (10 years 11 months 4 days 19 hours ago) and read 2710 times:

 45X20 . . . . . .
 Petertenthije From Netherlands, joined Jul 2001, 3560 posts, RR: 10 Reply 2, posted Sun Jun 5 2005 15:08:56 UTC (10 years 11 months 4 days 19 hours ago) and read 2704 times:

 30x30 = 120m fence the 45x20 given by Wunala gives you 130m fence
 Attamottamotta!
 Jan Mogren From Sweden, joined Dec 2000, 2043 posts, RR: 46 Reply 3, posted Sun Jun 5 2005 15:12:17 UTC (10 years 11 months 4 days 19 hours ago) and read 2701 times:

 But 30x30 isn't rectangular. /JM 36x25 is 122 meters fence[Edited 2005-06-05 15:14:58]
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 Aloges From Germany, joined Jan 2006, 9413 posts, RR: 39 Reply 4, posted Sun Jun 5 2005 15:17:58 UTC (10 years 11 months 4 days 19 hours ago) and read 2690 times:

 Quoting Jan Mogren (Reply 3):But 30x30 isn't rectangular.

Well, it's square - but a square is a rectangle, whereas a rectangle is not necessarily a square.

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 Petertenthije From Netherlands, joined Jul 2001, 3560 posts, RR: 10 Reply 5, posted Sun Jun 5 2005 15:17:59 UTC (10 years 11 months 4 days 19 hours ago) and read 2690 times:

 30,01 x 29,999 = 120 (only very slightly rectangular but still a rectangle)
 Attamottamotta!
 Jan Mogren From Sweden, joined Dec 2000, 2043 posts, RR: 46 Reply 6, posted Sun Jun 5 2005 15:30:51 UTC (10 years 11 months 4 days 19 hours ago) and read 2680 times:

 Way back I was taught that a square is not a rectangle, but never mind. You are probably correct. (30,01 x 29,999 = 900,2699 if one wants to argue   ) /JM
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 Kalakaua From United States of America, joined Jan 2004, 1516 posts, RR: 5 Reply 7, posted Sun Jun 5 2005 15:33:27 UTC (10 years 11 months 4 days 18 hours ago) and read 2675 times:

 Sounds like a classic Calc. I problem to me?
 Gravity explains the motions of the planets, but it cannot explain who set the planets in motion.
 Wunala From Australia, joined Mar 2005, 951 posts, RR: 0 Reply 8, posted Sun Jun 5 2005 15:59:06 UTC (10 years 11 months 4 days 18 hours ago) and read 2653 times:

 Quoting Kalakaua (Reply 7):Sounds like a classic Calc. I problem to me?

And your answer is ??????????????

 Backfire From Germany, joined Oct 2006, 0 posts, RR: 0 Reply 9, posted Sun Jun 5 2005 16:01:49 UTC (10 years 11 months 4 days 18 hours ago) and read 2654 times:

 Assume the parking lot is a rectangle with length x. Its width must therefore be 900/x Therefore the perimeter is twice the longer side plus twice the shorter side. Perimeter P = 2x + 2(900/x) Therefore P = 2x + 1800/x From this equation it can be seen that, if x is small, P becomes very high because of the second term. Similarly if x is large, P also becomes high because of the first term. In between there is a value of x for which P becomes a minimum (minimum P, of course, means the shortest fence and the least cost). To find the minimum of the P-x curve, you have to differentiate P with respect to x: P = 2x + 1800/x so: dP/dx = 2 - 1800/(x^2) The minimum of the P-x curve is the point at which the slope (dP/dx) is zero. Thus: 2 - 1800/(x^2) = 0 1800 = 2(x^2) (x^2) = 900 and therefore x = 30 So the length is 30 and the width is (900/x) ... also 30. It is indeed a square, but since a square is, by definition, rectangular, the problem is solved.
 IlikeYYC From United States of America, joined Dec 2003, 1373 posts, RR: 18 Reply 10, posted Sun Jun 5 2005 16:06:09 UTC (10 years 11 months 4 days 18 hours ago) and read 2645 times:

 Quoting Petertenthije (Reply 5):30,01 x 29,999 = 120 (only very slightly rectangular but still a rectangle)

I think that the questions means that it can not be a circle, triangle, pentagon, etc.- it has to have 4 perpendicular sides.

I have been taught that a square is a rectangle- just a special one.

 Fighting Absurdity with Absurdity!
 Kalakaua From United States of America, joined Jan 2004, 1516 posts, RR: 5 Reply 11, posted Mon Jun 6 2005 04:01:16 UTC (10 years 11 months 4 days 6 hours ago) and read 2541 times:

 Backfire has it... or at least has the jist of it. Other than that, everyone else is wrong!!!
 Gravity explains the motions of the planets, but it cannot explain who set the planets in motion.
 AirxLiban From Lebanon, joined Oct 2003, 4536 posts, RR: 52 Reply 12, posted Mon Jun 6 2005 04:08:43 UTC (10 years 11 months 4 days 6 hours ago) and read 2537 times:

 ditto Backfire in different terms... you are minimising Z=2x+2y where xy=900 so x=900/y so Z=2*(900/y)+2y Differentiate it... dZ/dy = 2-1800/y^2 Set it equal to zero, y=30 or y=-30 Since y=-30 does not make sense, we reject that solution and take y=30 Then x=300/y=300/30=30 So you need to go with 30x30.
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