Knewton Problem Solving

Question

The sum of the ages of Phil and Danielle is x years. If Phil is 10 years older than Danielle, how many years old will Danielle be x years from now, in terms of x?

A. x-5
B. 2x -5
C. 1/2x -5
D. 3/2x -5
E. 5/2x -5

adelabu44 · Answer

I got C but cant seem to find a way that will add up to D. Knewton kind of skipped the solution arriving to D.

fluke · Answer

Phil's present age: P
Danielle's present age: D

The sum of the ages of Phil and Danielle is x years
P+D=x--------------1

Phil is 10 years older than Danielle
P=D+10---------------2

Substituting 2 in 1:

D+10+D=x

2D=x-10

D=\frac{x-10}{2}

Q: how many years old will Danielle be x years from now?

D+x=\frac{x-10}{2}+x=\frac{x-10+2x}{2}=\frac{3x-10}{2}=\frac{3x}{2}-\frac{10}{2}=\frac{3}{2}x-5

Ans: "D"

jamifahad · Answer

Let the present age of Phil and Danielle be P and D respectively.
So, P+D=x ----(1)
Also, P=D+10 ----(2)

Substituting 2 in 1
D+10+D=x
2D+10=x
D=x-10/2. This is current age of Danielle in terms of x.
So, Danielle in x years will be D+x
= x-10/2 +x
=3x-10/2
=3/2x -5.

OA D.

StevenSzekeres · Answer

Although this may not be the most scientific method, I found it to be useful.

Suppose Danielle is 5 years old and Paul is 15.

This means that x=5+15=20

So, x years from now, Danielle will be 25 and we are asked to find out the relationship between her current age and her age in 20 years.

Now it is just a matter of reviewing the options given to determine which one explains this relationship.

Thus, 3/2x-5 =  -5 = 25 and so the answer is D.

adelabu44 · Answer

Thank you this place is so helpful. StevenSzekeres that really helped me a lot. As for the rest I realized that the addition of the x on the right side would make me have to find the LCD of 2 and multiply bot the top and bottom of x.

3 hours later and I get it lol

3 hours later and I get it lol

Spidy001 · Answer

Current X years from now
 
P = D+10 D+10+X

D D+X

also given P+D = X => D+10 +D = X
 => D = (X-10)/2

So x years from now ,Daniel would be (x-10)/2 + x years old = (3x/2)-5

Answer is D.

144144 · Answer

you can also solve this with plugging numbers.

P+D=x (ill plug in x=20)
so P+D=20

next we get info that P=D+10. so - D+10+D=20. so 2*D=10. So D=5, P=15.
the question is what will D+x equals. so we have 5+20 = 25.

if we look on the answers - we can see easy that the only answer is -
3*20/2-5 = 25!

answer is D.

Knewton Problem Solving

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards