rate problem !!!!!!!!!!pls help

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

Redeem

This topic has expert replies

Post new topic Post Reply

Previous Topic Next Topic

charmaine: Senior | Next Rank: 100 Posts; Posts: 71; Joined: Sun May 18, 2008 11:04 pm; Thanked: 1 times

rate problem !!!!!!!!!!pls help

by charmaine » Mon Jun 09, 2008 1:07 am

i do not know how it comes about ..i used algebra equation as solution bt it seems wrong

the time it took car P to travel 600 miles was 2 hrs less than the time it took car R to travel the same distance. if P's average speed was 10 miles per hour greater than that of car R, what was R's average speed, in miles per hour?

a. 40
b. 50
c. 60
d.70
e. 80
answer is b 50

thankssss

Quote

Source: Beat The GMAT — Problem Solving | Mon Jun 09, 2008 1:07 am

VerbalAttack: Junior | Next Rank: 30 Posts; Posts: 27; Joined: Mon May 26, 2008 9:34 pm; Thanked: 3 times

by VerbalAttack » Mon Jun 09, 2008 1:38 am

Hi Charmine,

assume the following;
tp = Time taken for Car P to travel 600miles
rp = Rate of Car P

tr = Time taken for Car R
rr = Rate of Car R

As per the question; tp = tr - 2 & rp = rr + 10

Use formula Rate = Distance / Time;

tp = 600 / rp and tr = 600 / rr

tp = 600 / rp ==> tr - 2 = 600 / (rr + 10) ==> replace tr with 600 / rr

==> after simplifying, we get ((6000/rr) - 2rr) = 20.

From here backsolve with answer choices.

You can also continue to solve the equation, which gives rr = -60 & rr = 50. As Rate can't be negative, take rr = 50.

Cheers

Quote

charmaine: Senior | Next Rank: 100 Posts; Posts: 71; Joined: Sun May 18, 2008 11:04 pm; Thanked: 1 times

by charmaine » Mon Jun 09, 2008 3:30 pm

thank you !

much appreciated

Quote

egybs: Master | Next Rank: 500 Posts; Posts: 178; Joined: Wed May 14, 2008 3:51 pm; Thanked: 16 times; Followed by:1 members; GMAT Score:99%+

by egybs » Mon Jun 09, 2008 3:50 pm

i did the same thing as verbalattack, but it seems messy. I think this is a perfect opportunity to just throw in numbers and not bother solving for p or r.

Quote

netigen: Legendary Member; Posts: 631; Joined: Mon Feb 18, 2008 11:57 pm; Thanked: 29 times; Followed by:3 members

by netigen » Mon Jun 09, 2008 4:36 pm

Back solving is idle here with a 30 sec soln but we can also try this the Maths way:

Tp = Tr - 2

600/Sp = (600/Sr) - 2

we know that Sp = 10 + Sr

600/(10+Sr) = (600/Sr) - 2

600/(10+Sr) = (600 - 2Sr)/Sr

600Sr = 6000+600Sr - 20Sr - 2(Sr^2)

2(Sr^2) + 20Sr - 6000 = 0

Sr^2 + 10Sr - 3000 = 0

Sr = -60 or Sr =50

since speed can not be -ve so Sr=50

Quote

GMAT/MBA Expert

Scott@TargetTestPrep: GMAT Instructor; Posts: 8088; Joined: Sat Apr 25, 2015 10:56 am; Location: Los Angeles, CA; Thanked: 43 times; Followed by:29 members

Re: rate problem !!!!!!!!!!pls help

by Scott@TargetTestPrep » Mon Aug 24, 2020 9:57 am

charmaine wrote: ↑
Mon Jun 09, 2008 1:07 am
i do not know how it comes about ..i used algebra equation as solution bt it seems wrong

the time it took car P to travel 600 miles was 2 hrs less than the time it took car R to travel the same distance. if P's average speed was 10 miles per hour greater than that of car R, what was R's average speed, in miles per hour?

a. 40
b. 50
c. 60
d.70
e. 80
answer is b 50

Solution:

Since the answer choices are easy numbers, let’s solve the problem numerically instead of algebraically. That is, we can check each answer choice until we find the correct answer.

If car R’s speed is 40 mph, then car P’s speed is 50 mph. Furthermore, it will take car R 600/40 = 15 hours and car P 600/50 = 12 hours to travel 600 miles. However, since 12 is not 2 less than 15, we see that choice A is not the correct answer.

If car R’s speed is 50 mph, then car P’s speed is 60 mph. Furthermore, it will take car R 600/50 = 12 hours and car P 600/60 = 10 hours to travel 600 miles. However, since 10 is 2 less than 12, we see that choice B is the correct answer.

Answer: B

Scott Woodbury-Stewart
Founder and CEO
[email protected]