BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

motion problem

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Junior | Next Rank: 30 Posts
Posts: 17
Joined: Sun Apr 06, 2008 12:04 pm

motion problem

by galit_d2d » Sun Apr 20, 2008 10:42 am
hi, I saw a problem in the math review document which is published in this forum.

gloria leaves home for school, riding her bicycle at the rate of 12mph 20 min later after she leaves her mother sees gloria's eng paper on her bed and leaves to bring it to her. If her mother drives at 36mph how far must she drives before she reaches gloria?

there is no answer just an equation which is:
12x= 36(x-1/3)
when :
x=time of gloria
x-1/3=time of the mother

I don't understand this...
somebody..help...
Top
Source: — Problem Solving |
Master | Next Rank: 500 Posts
Posts: 127
Joined: Sat Apr 19, 2008 1:02 am
Thanked: 12 times

by jasonc » Sun Apr 20, 2008 11:40 am
d=r*t (simple distance formula)
d = distance
r = rate/speed
t = time

question is asking you when will d of gloria = d of mother.

d of gloria = d of mother =>
r of gloria * t of gloria = r of mother * t of mother =>
12 * t = 36 (t - 1/3)

time is in hours since our rate/speed is in per hour. Therefore 20 min = 1/3 of 1 hour, so you subtract that from gloria's time to get the mother's time.
Top
User avatar
GMAT Instructor
Posts: 3225
Joined: Tue Jan 08, 2008 2:40 pm
Location: Toronto
Thanked: 1710 times
Followed by:614 members
GMAT Score:800

Re: motion problem

by Stuart@KaplanGMAT » Sun Apr 20, 2008 12:15 pm
galit_d2d wrote:hi, I saw a problem in the math review document which is published in this forum.

gloria leaves home for school, riding her bicycle at the rate of 12mph 20 min later after she leaves her mother sees gloria's eng paper on her bed and leaves to bring it to her. If her mother drives at 36mph how far must she drives before she reaches gloria?

there is no answer just an equation which is:
12x= 36(x-1/3)
when :
x=time of gloria
x-1/3=time of the mother

I don't understand this...
somebody..help...
This is a classic GMAT "catch up" question.

To answer this question, we want to do two things:

(1) figure out where the 1st person is when the 2nd person starts moving; and

(2) SUBTRACT their rates to find out how quickly the 2nd person is catching up.

Here:

Gloria has been traveling for 1/3 of an hour at 12mph.

Catch up distance = r*t = 12 * 1/3 = 4 miles

Catch up rate = Mom's rate - Gloria's rate = 36 - 12 = 24mph

So, the question becomes:

"How long does it take to travel 4 miles at 24mph?"

time = distance/rate = 4/24 = 1/6 of an hour = 10 minutes.
Image

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

Kaplan Exclusive: The Official Test Day Experience | Ready to Take a Free Practice Test? | Kaplan/Beat the GMAT Member Discount
BTG100 for $100 off a full course
Top
Master | Next Rank: 500 Posts
Posts: 127
Joined: Sat Apr 19, 2008 1:02 am
Thanked: 12 times

by jasonc » Sun Apr 20, 2008 1:12 pm
I forgot to mention that after you solve for t (total travel time for gloria), you'll get 30 min.

The question asks how far must the mother drive, so you need to take the time the mother drives (30 min - 20 min = 10 min = 1/6 hr) multiplied by her speed (36 mph) which will give you 6 miles.
Top
Junior | Next Rank: 30 Posts
Posts: 17
Joined: Sun Apr 06, 2008 12:04 pm

by galit_d2d » Sun Apr 20, 2008 1:54 pm
thank you I understood both ways:)
Top
Post new topic Post Reply
• Page 1 of 1