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In 10 years Linda will be as old as Bobby is now. Thirty years ago Bob

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In 10 years Linda will be as old as Bobby is now. Thirty years ago Bob  [#permalink]

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New post 23 Jan 2017, 09:45
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A
B
C
D
E

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80% (01:37) correct 20% (01:54) wrong based on 96 sessions

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Re: In 10 years Linda will be as old as Bobby is now. Thirty years ago Bob  [#permalink]

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New post 23 Jan 2017, 10:16
Harshit401 wrote:
C 40

Sent from my Lenovo A6020a46 using GMAT Club Forum mobile app

Am I Correct?

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In 10 years Linda will be as old as Bobby is now. Thirty years ago Bob  [#permalink]

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New post 23 Jan 2017, 10:17
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Re: In 10 years Linda will be as old as Bobby is now. Thirty years ago Bob  [#permalink]

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New post 23 Jan 2017, 11:44
Bunuel wrote:
In 10 years Linda will be as old as Bobby is now. Thirty years ago Bobby was twice Linda's age. How old is Linda now?

A. 20
B. 30
C. 40
D. 50
E. 60


Here is my solution:

L = B+10
B = 30-2(B+10)

L= 30-2(B+10)+10
L= 30-2B-20+10
2B= 20
B = 10

Linda = 10+10 = 20 Is it A ? please correct me if i am wrong :) thanks
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Re: In 10 years Linda will be as old as Bobby is now. Thirty years ago Bob  [#permalink]

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New post 23 Jan 2017, 11:48
Lets say Linda is 40 now ( Taken option C )
In 10 years Linda will be as old as Bobby is now : So in 10 years Linda will be 40+10= 50 years , so Bobby's age is 50 years now .

Thirty years ago Bobby was twice Linda's age : So Thirty years ago Linda's age was 40-30= 10 and Bobby's age 50-30 = 20 years .
Therefore we can see Bobby's age is twice as Linda's age .
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In 10 years Linda will be as old as Bobby is now. Thirty years ago Bob  [#permalink]

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New post 23 Jan 2017, 16:38
Bunuel wrote:
In 10 years Linda will be as old as Bobby is now. Thirty years ago Bobby was twice Linda's age. How old is Linda now?

A. 20
B. 30
C. 40
D. 50
E. 60


\(Linda + 10 = Bobby - (1)\)
\(Bobby - 30 = 2 (Linda - 30) - (2)\)

Substitute equation (1) into (2)

\(Linda + 10 - 30 = 2 Linda - 60\)
\(Linda = 60 + 10 - 30\)
\(Linda = 40\)

Answer : C. 40
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In 10 years Linda will be as old as Bobby is now. Thirty years ago Bob  [#permalink]

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New post 23 Jan 2017, 18:39
1
dave13 wrote:
Bunuel wrote:
In 10 years Linda will be as old as Bobby is now. Thirty years ago Bobby was twice Linda's age. How old is Linda now?

A. 20
B. 30
C. 40
D. 50
E. 60


Here is my solution:

L = B+10
B = 30-2(B+10)

L= 30-2(B+10)+10
L= 30-2B-20+10
2B= 20
B = 10

Linda = 10+10 = 20 Is it A ? please correct me if i am wrong :) thanks


The first equation is l+10 = b
The second equation is b-30 = 2(l-30) . Hence L = 40 Option C
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Re: In 10 years Linda will be as old as Bobby is now. Thirty years ago Bob  [#permalink]

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New post 23 Jan 2017, 22:14
Bunuel wrote:
In 10 years Linda will be as old as Bobby is now. Thirty years ago Bobby was twice Linda's age. How old is Linda now?

A. 20
B. 30
C. 40
D. 50
E. 60



Apart from the checking choices and proper method, another logical way to look at the Q..

In 10 years Linda will be as old as Bobby is now. MEANS difference in age is 10.

Thirty years ago Bobby was twice Linda's age.
if the difference is 10, doubling can be ONLY when the younger is EQUAL to this difference, 10
If I have to make an equation..
Age of younger is x, so age of elder will be x+10..
Now 2x=(x+10)... x=10..
Present age =30+10=40..
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Re: In 10 years Linda will be as old as Bobby is now. Thirty years ago Bob  [#permalink]

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New post 24 Jan 2017, 01:00
Bunuel wrote:
In 10 years Linda will be as old as Bobby is now. Thirty years ago Bobby was twice Linda's age. How old is Linda now?

A. 20
B. 30
C. 40
D. 50
E. 60



<== 30 years------Now----10 years==>

I will eliminate answer A & B ...if she is 20 or 30 years now, then she wasn't born yet 30 years ago.

by trying answer choice (c)

L+10=B (1) ==> 40+10 =50
B=50 from (1) (now)

B-30=2(L-30) ==> 50-30 = 2(40-30)

which means...30 years ago B was 20 and L was 10

Answer is C (40)
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Re: In 10 years Linda will be as old as Bobby is now. Thirty years ago Bob  [#permalink]

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New post 24 Jan 2017, 02:08
laddaboy wrote:
dave13 wrote:
Bunuel wrote:
In 10 years Linda will be as old as Bobby is now. Thirty years ago Bobby was twice Linda's age. How old is Linda now?

A. 20
B. 30
C. 40
D. 50
E. 60


Here is my solution:

L = B+10
B = 30-2(B+10)

L= 30-2(B+10)+10
L= 30-2B-20+10
2B= 20
B = 10

Linda = 10+10 = 20 Is it A ? please correct me if i am wrong :) thanks


The first equation is l+10 = b
The second equation is b-30 = 2(l-30) . Hence L = 40 Option C


i got it, many thanks for taking time to correct me - laddaboy :)
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Re: In 10 years Linda will be as old as Bobby is now. Thirty years ago Bob  [#permalink]

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New post 27 Jan 2017, 10:34
1
Bunuel wrote:
In 10 years Linda will be as old as Bobby is now. Thirty years ago Bobby was twice Linda's age. How old is Linda now?

A. 20
B. 30
C. 40
D. 50
E. 60



We can let L = Linda’s age today and B = Bobby’s age today.

We are given that in 10 years Linda will be as old as Bobby is now. Thus:

10 + L = B

We are also given that thirty years ago Bobby was twice Linda's age, thus:

B - 30 = 2(L - 30)

B - 30 = 2L - 60

B = 2L - 30

Since B = 2L - 30, we can substitute 2L - 30 for B in the equation 10 + L = B and we have:

10 + L = 2L - 30

40 = L

Answer: C
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Re: In 10 years Linda will be as old as Bobby is now. Thirty years ago Bob  [#permalink]

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Re: In 10 years Linda will be as old as Bobby is now. Thirty years ago Bob   [#permalink] 16 Sep 2018, 18:52
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