Wikipedia:Reference desk/Archives/Mathematics/2006 October 27

Welcome to the Wikipedia Mathematics Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

October 27

Conundrum

I am as old as Casey will be when I am twice as old as Casey

was when my age was half the sum of our present ages.

Casey is as old as I was when Casey was

half the age he will be 10 years from now.

How old am I?

Can anyone help? MusicMan1015 02:13, 27 October 2006 (UTC)

You don't know how old you are? Sorry, I can't help. (Check your birth certificate.) You want someone else to do your homework for you? Sorry, the instructions at the top of this page say don't ask here. Want help with algebra? Ask something specific, showing you've put in some effort of your own. Want a hint? Let a be your age and let c be Casey's age. Translate the two sentences into equations in a and c; standardize as a system of linear equations. --KSmrq^T 02:56, 27 October 2006 (UTC)

It's not HW. I'm well aware of the rules. MusicMan1015 03:21, 27 October 2006 (UTC)

I'll get you started:

 C      = Casey's current age               C+10    = Caseys age 10 years from now
   M    = My current age                   (C+10)/2 = Half Caseys age 10 years from now
 C+M    = Sum of our current ages
(C+M)/2 = Half the sum of our current ages

Continue like this and show us all your assignments, then we may help some more. StuRat 03:36, 27 October 2006 (UTC)

To be fair, the wording is a bit tricky. Maybe this will help:

I am as old (as Casey will be when I am (twice as old (as Casey was when my age was (half the sum of our present ages))))).

Casey is as old (as I was when Casey was (half the age Casey will be 10 years from now)).

Start by translating what's in parentheses, then work your way out in stages. There are three numbers worth keeping in mind: your age now, Casey's age now, and the difference between them (which is constant as you age). You'll wind up with two pretty simple formulas in two variables (C and M), which you can solve if you've learned Algebra. Black Carrot 21:25, 27 October 2006 (UTC)

When you've worked that one out, you can try your new-found skills on this one:

• Ten years from now, Tim will be twice as old as Jane was when Mary was nine times as old as Tim. Eight years ago, Mary was half as old as Jane will be when Jane is one year older than Tim will be at the time when Mary will be five times as old as Tim will be two years from now. When Tim was one year old, Mary was three times as old as Tim will be when Jane is three times as old as Mary was six years before the time when Jane was half as old as Tim will be when Mary will be ten years older than Mary was when Jane was one third as old as Tim will be when Mary wil be three times as old as she was when Jane was born. How old are they all now? JackofOz 11:57, 30 October 2006 (UTC)

ultra-elliptical functions

I really need to know what ultra-elliptical functions is. Can somebody please explain this to me? —The preceding unsigned comment was added by 213.64.69.132 (talk • contribs) .

They seem to be due to Sofia Kovalevskaya (Sophia Kovalevsky}; our article mentions the publication Mémoire sur un cas particulier du problème de le rotation d'un corps pesant autour d'un point fixe, ou l'intégration s'effectue à l'aide des fonctions ultraelliptiques du temps (1886). Another source gives this reference: "Memoirs présentés par divers savants étrangers à l'Académie des Sciences de l'Institut National de France". Paris. 1890. V.31. p.1–62. The term does not appear to have gained much currency.  --Lambiam^Talk 21:08, 27 October 2006 (UTC)

MU key in calculator

MU stands for Mark Up, which is for calculating Gross margin used in business environments. There are different methods of calculating this, depending on the model of the calculator.
Below some examples that works with my calculator:

Example 1: Enter 100 then press the divide key, then enter 15 then press the MU key, which displays 117.65 (15% of this total equates to 17.65)
Example 2: Enter 125 (selling price) then press the minus key, then enter 100 (seller's costs) then press the MU key, which displays 25 (25% Gross margin)