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Re: Exactly 8 years ago, Jim’s son was twice as old as Jim’s daughter. If [#permalink]

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23 Oct 2017, 10:11

-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.
_________________

I'd love to hear any feedback or ways to improve my problem solving. I make a lot of silly mistakes. If you've had luck improving on stupid mistakes, I'd love to hear how you did it.

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

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
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Scott Woodbury-Stewart Founder and CEO

GMAT Quant Self-Study Course 500+ lessons 3000+ practice problems 800+ HD solutions

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

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26 Oct 2017, 02:49

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