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Frank is 15 years younger then John. In 5 years John will be

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Joined: 07 Aug 2011
Posts: 51
Concentration: Entrepreneurship, Finance
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Frank is 15 years younger then John. In 5 years John will be  [#permalink]

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11 Mar 2012, 14:54
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5% (low)

Question Stats:

86% (01:46) correct 14% (01:32) wrong based on 245 sessions

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Frank is 15 years younger then John. In 5 years John will be twice as old as Frank. How old will Frank be in four years?

A. 8
B. 10
C. 12
D. 14
E. 16
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Joined: 02 Sep 2009
Posts: 49320
Re: Fank is 15 years younger than John....  [#permalink]

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11 Mar 2012, 15:04
1
Stoneface wrote:
Frank is 15 years younger then John. In 5 years John will be twice as old as Frank. How old will Frank be in four years?

a 8
b 10
c 12
d 14
e 16

Frank is 15 years younger then John --> F+15=J;

In 5 years John will be twice as old as Frank (in 5 year John will be J+5 years old and Frank will be F+5 years old) --> J+5=2*(F+5) --> (F+15)+5=2*(F+5) --> F=10;

In 4 years Frank will be 10+4=14 years old.

Hope it's clear.
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Re: Frank is 15 years younger then John. In 5 years John will be  [#permalink]

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11 Mar 2012, 15:34
This is where I made my mistake: J+5=2*(F+5). I was working J+5=2*F. Thanks!
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Re: Frank is 15 years younger then John. In 5 years John will be  [#permalink]

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13 Mar 2012, 16:32
I like to work these kind of problems in columns

F | J
----------------------
Now X-15 | X

In 5 years X-15+5=X-10 | X+5

twice as old means X+5=X-10=>X=25

But what we want is X-15+4 so 25-15+4=D

PS: The column is not clear enough in the post but I hope it is obvious
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Re: Frank is 15 years younger then John. In 5 years John will be  [#permalink]

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07 Jan 2017, 15:26
F = J-15
2(F+5) = J+5 >> 2F+10=J+5

So. F= 10

In four years,

F+4=14
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Re: Frank is 15 years younger then John. In 5 years John will be  [#permalink]

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18 Aug 2018, 19:21
Stoneface wrote:
Frank is 15 years younger then John. In 5 years John will be twice as old as Frank. How old will Frank be in four years?

A. 8
B. 10
C. 12
D. 14
E. 16

We can create the equations:

F + 15 = J

and

J + 5 = 2(F + 5)

J + 5 = 2F + 10

J = 2F + 5

Substituting, we have:

F + 15 = 2F + 5

10 = F

So in 4 years Frank will be 14.

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Frank is 15 years younger then John. In 5 years John will be  [#permalink]

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19 Aug 2018, 00:59
Stoneface wrote:
Frank is 15 years younger then John. In 5 years John will be twice as old as Frank. How old will Frank be in four years?

A. 8
B. 10
C. 12
D. 14
E. 16
Attachment:

Capture.PNG [ 3.18 KiB | Viewed 541 times ]

$$j + 5 = 2(j - 10)$$

$$j + 5 = 2j - 20$$

Or, $$j = 25$$ ,

So, Frank's age after 4 years will be $$j - 11$$ , ie $$25 - 11 = 14$$, Answer must be (D)
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