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the_beaver
Joined: 15 Jan 2003
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 Posted: Mon May 15, 2006 3:32 am Post subject: solve and explain |
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Five years ago a woman was six times as old as her son.
Four years from now, she will be three times as old as the boy.
The age of the son is _________ now.
A co-worker sent me this and I know the answer, but I got in a stupid way (plugging in random numbers until something worked) -- can anybody show me how to work this out in actual steps using actual logic? |
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Lizara
Joined: 14 Apr 2004
Location: Seoul
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| Posted: Mon May 15, 2006 3:46 am Post subject: |
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y is the woman's current age, x is the son's current age...
y-5=6(x-5)
y+4=3(x+4)
y-5=6x-30
y+4=3x+12
y=6x-25
y=3x+8
6x-25=3x+8
3x=33
x=11
y=3x+8=41
Fear my uberl33t algebra skills! woo!
/sarcasm |
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kermo
Joined: 01 Sep 2004
Location: Eating eggs, with a comb, out of a shoe.
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| Posted: Mon May 15, 2006 3:47 am Post subject: |
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| Lizara wrote: |
y is the woman's current age, x is the son's current age...
y-5=6(x-5)
y+4=3(x+4)
y-5=6x-30
y+4=3x+12
y=6x-25
y=3x+8
6x-25=3x+8
3x=33
x=11
y=3x+8=41
Fear my uberl33t algebra skills! woo!
/sarcasm |
Nice-uh!
Yep, that's what I woulda done. |
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schwa
Joined: 18 Jan 2003
Location: Yap
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| Posted: Mon May 15, 2006 3:48 am Post subject: |
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Maybe the equation would look like this:
6(x - 5) = 3(x + 4)
But I dont know how you'd solve for x -- I flunked math. |
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flotsam
Joined: 28 Mar 2006
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| Posted: Mon May 15, 2006 3:55 am Post subject: |
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| Nerds. |
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kermo
Joined: 01 Sep 2004
Location: Eating eggs, with a comb, out of a shoe.
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| Posted: Mon May 15, 2006 4:00 am Post subject: |
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| schwa wrote: |
Maybe the equation would look like this:
6 X (x - 5) = 3 X (x + 4)
But I dont know how you'd solve for x -- flunked math. |
Oooh, snazzy. Let me have a look at that...
Okay, wait. There's a much easier way.
I'm working on it. I just made it work, then utterly confuzzled myself. Give me another minute.
Yep, I pretty much had the son's age at -3. I'm a freakin' genius.
Last edited by kermo on Mon May 15, 2006 4:03 am; edited 1 time in total |
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kermo
Joined: 01 Sep 2004
Location: Eating eggs, with a comb, out of a shoe.
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| Posted: Mon May 15, 2006 4:02 am Post subject: |
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| schwa wrote: |
Maybe the equation would look like this:
6(x - 5) = 3(x + 4)
But I dont know how you'd solve for x -- I flunked math. |
Okay- that didn't work because the brackets are in the wrong place. I tried something similar, but then I looked at Brainy Smurf over there (Lizara) and realized that her son's age isn't a constant. It changes when her age changes. Duh. |
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flotsam
Joined: 28 Mar 2006
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| Posted: Mon May 15, 2006 4:04 am Post subject: |
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| kermo wrote: |
| schwa wrote: |
Maybe the equation would look like this:
6 X (x - 5) = 3 X (x + 4)
But I dont know how you'd solve for x -- flunked math. |
Oooh, snazzy. Let me have a look at that...
Okay, wait. There's a much easier way.
I'm working on it. I just made it work, then utterly confuzzled myself. Give me another minute. |
I'm stealing this word. |
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Privateer
Joined: 31 Aug 2005
Location: Easy Street.
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| Posted: Mon May 15, 2006 4:04 am Post subject: Re: solve and explain |
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| the_beaver wrote: |
Five years ago a woman was six times as old as her son.
Four years from now, she will be three times as old as the boy.
The age of the son is _________ now.
A co-worker sent me this and I know the answer, but I got in a stupid way (plugging in random numbers until something worked) -- can anybody show me how to work this out in actual steps using actual logic? |
It's simultaneous equations.
x = the woman's age
y = her son's age
x - 5 = 6(y - 5) --> x = 6y - 25
x + 4 = 3(y + 4) --> x = 3y + 8
Hence, 6y - 25 = 3y + 8 --> 3y = 33 --> y = 11
That makes x = 41
The woman is 41 now and her son is 11.
[edit]Oh I see while I was working that out about 6 people posted.  [/edit] |
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midgic
Joined: 14 Feb 2004
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| Posted: Mon May 15, 2006 5:43 am Post subject: |
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| Quote: |
6(x - 5) = 3(x + 4)
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If x is the son's age now:
6(x - 5) = the woman's age five years ago
3(x + 4) = the woman's age four years from now
The woman's age five years ago PLUS NINE = the woman's age four years from now...
So, 6(x - 5) + 9 = 3(x + 4)
6x -30 + 9 = 3x + 12
3x - 21 = 12
3x = 33
x = 11
So, the son's age now is 11. |
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EFLtrainer
Joined: 04 May 2005
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| Posted: Wed May 17, 2006 6:17 pm Post subject: |
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| Thanks, midgic, cause I thought I'd lost my mind with people posting that 41 is three times more than 11!!! |
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