# Lisa is older than...

• Feb 22nd 2013, 08:01 AM
Paze
Lisa is older than...
Lisa is four times older than Anne.

In 5 years, Lisa will be 3 times older than Anne.

How old are Lisa and Anne?

I've tried setting it up two ways: $y=4x\\y+5=3x$ and then solving for x which grants me x=-5.

I've also tried $4x+5=3x$ which also delivers the answer x=-5. Obviously Anne is not -5 years old.

Thank you :)
• Feb 22nd 2013, 08:11 AM
heaviside
Re: Lisa is older than...
The first equation is correct. I think you want $y+5 = 3(x+5)$ for the second equation.
• Feb 22nd 2013, 08:13 AM
Paze
Re: Lisa is older than...
I get the answer -5. How is that correct?

Thank you.
• Feb 22nd 2013, 08:15 AM
heaviside
Re: Lisa is older than...
The first equation I am referring to is $y=4x$. To summarize, the equations are $y=4x$ and $y+5=3(x+5)$. So x=10.
• Feb 22nd 2013, 08:22 AM
Paze
Re: Lisa is older than...
Quote:

Originally Posted by heaviside
The first equation I am referring to is $y=4x$. To summarize, the equations are $y=4x$ and $y+5=3(x+5)$. So x=10.

Ah, I see. Thank you!
• Feb 22nd 2013, 12:06 PM
HallsofIvy
Re: Lisa is older than...
Notice that the question asked "How old are Lisa and Anne". Just answering "x= 10" would NOT be acceptable. You started by saying that "Lisa is four times older than Anne" turned into y= 4x so apparently you are saying that Annes current age is 10 and Lisa's current age is 4(10)= 40.

By the way, I would argue that y= 4x would be "Lisa is four times as old as Anne". I would interpret "Lisa is four times older than Anne" as meaning that the difference between Anne and Lisa's age is four times Anne's age. That would translate to y- x= 4x or y= 5x.
• Feb 22nd 2013, 12:10 PM
Paze
Re: Lisa is older than...
Quote:

Originally Posted by HallsofIvy
Notice that the question asked "How old are Lisa and Anne". Just answering "x= 10" would NOT be acceptable. You started by saying that "Lisa is four times older than Anne" turned into y= 4x so apparently you are saying that Annes current age is 10 and Lisa's current age is 4(10)= 40.

By the way, I would argue that y= 4x would be "Lisa is four times as old as Anne". I would interpret "Lisa is four times older than Anne" as meaning that the difference between Anne and Lisa's age is four times Anne's age. That would translate to y- x= 4x or y= 5x.

Yea, sorry about the grammatical errors. I am translating the question from my own language :) Thank you.