Wikipedia:Reference desk/Archives/Mathematics/2006 October 30

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October 30

history of the compass

I am trying to find information on (geometry) compasses for a school project for my son and am having trouble finding info on the history of them. Ie: where they come from, who made them etc. Any links or info would be appreciated. Kerry. --203.58.44.15 03:45, 30 October 2006 (UTC)

The third postulate of Euclid's Elements: "Given a straight line segment, a circle can be drawn using the segment as radius and one endpoint as center", shows that the compass was known circa 300 BC. Presumably it is much and much older as an instrument to transfer a reference length. This web site states: "[The Egyptian god] Ptah's major symbols are the Masonic Square and Compass, encircled by a knotted length of rope." I don't know how reliable that site is, and could not find further corroboration of this statement, but by itself it is plausible that the ancient Egyptians knew the compass. If made of wood, you don't expect much of these to have survived 50 centuries or so, even in a desert climate. Since it does not require particularly advanced skills to make a compass, it would not be strange if not much is known about their early history.  --Lambiam^Talk 04:44, 30 October 2006 (UTC)

Sorry, should I say "this web site and only this web site" ? None else found searching "Ptah + compass". His attributes are : an ankh, a djed, and a was scepter. Are these masonic fans rewriting Egyptian history ? -- DLL ^{.. T} 19:49, 30 October 2006 (UTC)

Thanks Lambiam, the information you have shown will be more than adequate for his project. The pictures supported with information is far more than others in his class have been able to find. Much appreciated. Kerry --203.58.44.15 20:56, 30 October 2006 (UTC)

Value of a Life Estate

When my uncle dies he is leaving his $350,000 home to his 65 year old friend.

When his friend dies or moves out, the home will go to me, according to my Uncle's Will.

What might I have to pay his friend to encourage her to move now (the value of the Life Estate)?

Thank you.

It sounds like all the friend gets is the use of the home (as opposed to ownership), for the remainder of their life. If we figure a life expectancy of 85, and a value of US$15,000 per year, that would be US$300,000. Unfortunately, with taxes and other transaction costs, this would make that too much money to pay. Of course, you would know more about this person's health and the rental prices for a comparable house in your area, so could come up with a more accurate estimate. We could have attempted to take inflation during the 20 years into account, as well, but that would more or less even out if it was invested such that it returned the rate of inflation, after taxes. Also note that many people are rather short-sighted, and would take a much smaller amount of cash NOW, rather than a larger sum later. StuRat 14:22, 30 October 2006 (UTC)

Note that I was assuming your uncle dies now. If we have to take his life expectancy into account relative to his friends, then things get complicated. The value to his friend might be almost zero, if your uncle is likely to outlive the friend. Another thought, perhaps you could pay the friend somewhat less, but still allow him to live in a portion of the house, with the rest available for you. This might work out better financially for both of you. StuRat 14:29, 30 October 2006 (UTC)

You don't need to use mathematics, you can find out using this method.

(1) Determine the max value that the house is worth to you right now. Say $80,000

(2) Tell your uncle, you will start at $1000 and increase by $1000 every time but do not tell him your max value.

(3) If at anytime, he says "I accept" then that is the correct value.

(4) If you reach your max value ($80,000) then the entire deal is off.

Your uncle would have to decide how much the use of the house is worth to him. As long as it is worth less than your MAX value, he will accept your offer. If it is over your MAX value then you might as well wait until he dies. 202.168.50.40 00:21, 31 October 2006 (UTC)