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

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AAPL: Moderator; Posts: 2599; Joined: Sun Oct 29, 2017 2:08 pm; Followed by:2 members

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

by AAPL » Sat Dec 23, 2017 2:42 pm

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

The OA is C.

I don't have clear this PS question, but I think that I can solve it of the following way,

I have this equation B=L+10, where B, is Bobby's age and L is Linda's age.

Then I have 2*L=B-30.

I have an equations system of 2 equations with 2 incognits, right?

I appreciate if any expert explain it for me. Thank you so much.

Quote

Source: Beat The GMAT — Problem Solving | Sat Dec 23, 2017 2:42 pm

GMATWisdom: Master | Next Rank: 500 Posts; Posts: 100; Joined: Wed Nov 29, 2017 4:38 pm; Thanked: 14 times

by GMATWisdom » Sat Dec 23, 2017 6:48 pm

AAPL 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

The OA is C.

I don't have clear this PS question, but I think that I can solve it of the following way,

I have this equation B=L+10, where B, is Bobby's age and L is Linda's age.

Then I have 2*L=B-30.

I have an equations system of 2 equations with 2 incognits, right?

I appreciate if any expert explain it for me. Thank you so much.

Sir your first equation B= L+10 is ok assuming Lindas and Bobbys present age as L and B
but your second equation is wrong because 30 years ago Lindas age would be L-30.
So the correct equation would be 2*(L-30)= B-30.
Putting B=L+10 in the equation we get 2*(L-30) =L+10 -30
Solving this we get L=40
Hence option C is correct

Quote

GMAT/MBA Expert

Scott@TargetTestPrep: GMAT Instructor; Posts: 8086; Joined: Sat Apr 25, 2015 10:56 am; Location: Los Angeles, CA; Thanked: 43 times; Followed by:29 members

by Scott@TargetTestPrep » Mon Sep 09, 2019 9:49 am

AAPL 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 B = Bobby's current age and L = Linda's current age; thus:

L + 10 = B

and

(L - 30) * 2 = (B - 30)

2L - 60 = B - 30

2L - 30 = B

Substituting, we have:

2L - 30 = L + 10

L = 40

Answer: C

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