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# Susan is now 10 years younger than Jane. If in five years,

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Susan is now 10 years younger than Jane. If in five years, [#permalink]

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05 Apr 2006, 07:39
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

Susan is now 10 years younger than Jane. If in five years, Jane will be twice as old as Susan, how old will Susan be in 3 years?

I have a hard time setting up these equations and would appreciate if someone can walk we through it and give me a sure fire way to always get these right.

I never know where to add the "in five years part" and i always screw them up.

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05 Apr 2006, 07:43
Susan is now 10 years younger than Jane. If in five years, Jane will be twice as old as Susan, how old will Susan be in 3 years?

Let's work it through.

Consider Susan's and Jane's age today as S and J respectively. The equation for today then is: S+10=J

In the future, their ages will be S+5 and J+5. The equation is then:
(J+5)=2(S+5)

Another way to think about this is to say the normal equation J=2S, and then think logically that those variables are different from today's variables by 5 years.

2S+5 = J
2S+5 = S+10
S= 5

In three years, Susan will be 8.
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05 Apr 2006, 10:45
I also had a lot of trouble with this.

I think the key is to keep in mind that any age in the future is
the age today + the # of years in the future. In your example, S+5 and J+5.
Notice that when you add 5, you have to add 5 to both subject S and J to keep the relationship.
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06 Apr 2006, 00:23
Try doing this:

-------Past --- Present --- Future (5 years time)
Susan ----------- x-10 -------x-5
Jane ------------- x ---------x+5

So we know (x-5)2 = (x+5)
2x-10 = x+5
x = 15

So Susan is 5 years old now, and 8 year old 3 years from now
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06 Apr 2006, 12:46
8 years

Use all the time scale separately

Now s+10=j

after x year , add x to both and j

Before x years deduct x in both s and j...

ywilfred wrote:
Try doing this:

-------Past --- Present --- Future (5 years time)
Susan ----------- x-10 -------x-5
Jane ------------- x ---------x+5

So we know (x-5)2 = (x+5)
2x-10 = x+5
x = 15

So Susan is 5 years old now, and 8 year old 3 years from now
06 Apr 2006, 12:46
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