Exactly 8 years ago, Jim’s son was twice as old as Jim’s daughter. If

Question

Exactly 8 years ago, Jim’s son was twice as old as Jim’s daughter. If Jim’s son is now 5 years older than his daughter, how old is Jim’s daughter now?

(A) 5
(B) 10
(C) 13
(D) 16
(E) 18

ewmike · Answer

Let jim daughter be d
Jim son be x
X-8=2d-8
X=d+5
d+5-8=2d-8
d-3=2d-d
d=5
A is correct

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Jashan79 · Answer

EQ 1 Jim's son = S
 Jim's Daughter = D
 
 (S-8)= 2 (D-8)
 S-8 = 2D- 16
 S-2D= -8
EQ2 S= D+5 or S- D = 5
 
Equating eq 1 and 2

D=13

qic032 · Answer

s=son's age now
d=daughter's age now

(s-8)/(d-8)=2
s-d=5

solve about equations:
d=13 (C)

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generis · Answer

Exactly 8 years ago, Jim’s son, S, was twice as old as Jim’s daughter, D

S - 8 = 2(D - 8)

Son is now five years older than daughter:

S = D + 5
Substitute for S in first equation

(D + 5) - 8 = 2(D - 8)
D - 3 = 2D - 16
D = 13

(Check: D is 13 now; 8 years she ago was 5. S is 18 now (= D + 5), so 8 years ago he was 10. 10 = twice as old as 5, back then. Correct.)

Answer C

Mo2men · Answer

Hi, 
There is an errot here. You did not mulyply 2 * 8 too. it should be

2 (d -8) = 2d - 16

Plunkster82 · Answer

-I set the original equation up as (s-8)=2(d-16), which simplifies to s-8=2d-16. 
-we are given s=d+5, so I substitute that in for s. 
-d-3=2d-16, simplified d=13.

Initially, I made a small mistake and got d=5, quickly checking my math, I realized the daughter cannot be 5 because 8 years ago she wasn't born yet. So I redid it until I figured out my mistake. I wasted a lot of time on something pretty simple here.

Simple mistakes are my biggest problem, I know the material pretty well, but I just make a lot of dumb errors. Any guidance would be appreciated.

N19 · Answer

If Son = X
Daughter=X-5

EQ: x-8=2(X-5-8)
X-8=2X-26
X=18

Daughter = 18-5= 13

Answer is C

ScottTargetTestPrep · Answer

We can let Jim’s son’s current age = s and Jim’s daughter’s current age = d. We can also state that 8 years ago, his son was (s - 8) years old and his daughter was (d - 8) years old. We can create the following equation:

s - 8 = 2(d - 8)

s - 8 = 2d - 16

s = 2d - 8

and

s = 5 + d

Thus:

2d - 8 = 5 + d

d = 13

Answer: C

gps5441 · Answer

we can also check from answer choices if we are unable to form the equation.
Start from C
Let Jim's daughter's age be 13 today
Jim's son age today will be 13+5=18
Now 8 years ago the son was 2 times the age of the daughter.
find the age of both of them 8 years ago
Daughter=13-8=5
Son=18-8=10
Now 10 =2x5=10=Answer C

BrentGMATPrepNow · Answer

Jim’s son is now 5 years older than his daughter  
Let D = the daughter's age NOW 
So D + 5 = the son's age NOW

This also means that  D - 8  = the daughter's age EIGHT YEARS AGO
This also means that D + 5 - 8 = the son's age EIGHT YEARS AGO
Or we can say,  D - 3  = the son's age EIGHT YEARS AGO

8 years ago, Jim’s son was twice as old as Jim’s daughter.  
8 years ago, the daughter's age was  D - 8  and the son's age was  D - 3 
So, we can write:  D - 3  = 2( D - 8 )
Expand right side to get: D - 3 = 2D - 16
Solve to get D = 13

Since D = the daughter's present age, the correct answer is C

Cheers,
Brent

fskilnik · Answer

? = D

\left\{ \begin{gathered}
 \left( {S - 8} ight) = 2\left( {D - 8} ight) \hfill \
 S = D + 5 \hfill \ 
\end{gathered} ight.\,\,\,\,\,\,\,\, \sim \,\,\,\,\,\,\,\left\{ \begin{gathered}
 \left( {S - 8} ight) = 2\left( {D - 8} ight) \hfill \
 \left( {S - \underline 8 } ight) = \left( {D - \underline 8 } ight) + 5 \hfill \ 
\end{gathered} ight.\,\,\,\,\,\,\,\,\mathop \Rightarrow \limits^{\left( {\, - \,} ight)} \,\,\,\,\,\,\,\,\left( {D - 8} ight) - 5 = 0\,\,\,\,\,\,\,\, \Rightarrow \,\,\,\,\,\,? = D = 13

The above follows the notations and rationale taught in the GMATH method.

bumpbot · Answer

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