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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] New post 05 Apr 2006, 07:39
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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.

Thanks in advance for your help.

Adam
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 [#permalink] New post 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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 [#permalink] New post 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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 [#permalink] New post 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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 [#permalink] New post 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
  [#permalink] 06 Apr 2006, 12:46
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Susan is now 10 years younger than Jane. If in five years,

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