January 22, 2019 January 22, 2019 10:00 PM PST 11:00 PM PST In case you didn’t notice, we recently held the 1st ever GMAT game show and it was awesome! See who won a full GMAT course, and register to the next one. January 26, 2019 January 26, 2019 07:00 AM PST 09:00 AM PST Attend this webinar to learn how to leverage Meaning and Logic to solve the most challenging Sentence Correction Questions.
Author 
Message 
TAGS:

Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 52390

Myra drove at an average speed of 30 miles per hour for some time and
[#permalink]
Show Tags
06 Apr 2015, 06:25
Question Stats:
67% (01:43) correct 33% (02:16) wrong based on 323 sessions
HideShow timer Statistics




Retired Moderator
Joined: 06 Jul 2014
Posts: 1231
Location: Ukraine
Concentration: Entrepreneurship, Technology
GMAT 1: 660 Q48 V33 GMAT 2: 740 Q50 V40

Re: Myra drove at an average speed of 30 miles per hour for some time and
[#permalink]
Show Tags
06 Apr 2015, 06:51
Bunuel wrote: Myra drove at an average speed of 30 miles per hour for some time and then at an average speed of 60 miles/hr for the rest of the journey. If she made no stops during the trip and her average speed for the entire journey was 50 miles per hour, for what fraction of the total time did she drive at 30 miles/hour?
(A) 1/5 (B) 1/3 (C) 2/5 (D) 2/3 (E) 3/5
Kudos for a correct solution. Let's name first part of distance F and second part S We can make weighted average equation: 0.3F + 0.6S = 0.5(S + F) 0.1S=0.2F \(\frac{S}{F}=\frac{2}{1}\) So First part equal to \(\frac{1}{3}\) of all time Answer is B
_________________
Simple way to always control time during the quant part. How to solve main idea questions without full understanding of RC. 660 (Q48, V33)  unpleasant surprise 740 (Q50, V40, IR3)  antidebrief




Manager
Joined: 27 Dec 2013
Posts: 237

Re: Myra drove at an average speed of 30 miles per hour for some time and
[#permalink]
Show Tags
06 Apr 2015, 07:00
my answer is 1/3. Let the total distance be 1. The distance covered on 30mph= x; so the distance covered on 60 will be 1x <> X (1x) Equating times, x/30 + 1x/60 = 1/50; Solving we get, X= 1/5.= so distance covered at 30mph=1/5 and distance covered at 60mph=4/5 Time calculation, Time taken to cover 1/5 jounery at 30mph= 1/150. Total time taken for the entire jouney= 1/50. Fraction of the time. 1/150/1/50 = 1/3 (option B). Please correct me if wrong. Bunuel wrote: Myra drove at an average speed of 30 miles per hour for some time and then at an average speed of 60 miles/hr for the rest of the journey. If she made no stops during the trip and her average speed for the entire journey was 50 miles per hour, for what fraction of the total time did she drive at 30 miles/hour?
(A) 1/5 (B) 1/3 (C) 2/5 (D) 2/3 (E) 3/5
Kudos for a correct solution.
_________________
Kudos to you, for helping me with some KUDOS.



Director
Joined: 07 Aug 2011
Posts: 532
Concentration: International Business, Technology

Re: Myra drove at an average speed of 30 miles per hour for some time and
[#permalink]
Show Tags
06 Apr 2015, 07:57
Bunuel wrote: Myra drove at an average speed of 30 miles per hour for some time and then at an average speed of 60 miles/hr for the rest of the journey. If she made no stops during the trip and her average speed for the entire journey was 50 miles per hour, for what fraction of the total time did she drive at 30 miles/hour?
(A) 1/5 (B) 1/3 (C) 2/5 (D) 2/3 (E) 3/5
Kudos for a correct solution. very simple application of weight average 305060 W. Avg is 20 unit far from 30 and 10 unit far from 60 so So at 60 mph she drove 2/3 of distance and at 30 mph she drove 1/3 of the distance. Answer b



Manager
Joined: 17 Mar 2014
Posts: 227
Location: India
Concentration: Operations, Strategy
GPA: 3.19
WE: Information Technology (Computer Software)

Myra drove at an average speed of 30 miles per hour for some time and
[#permalink]
Show Tags
06 Apr 2015, 08:04
5030=20 6050=10 Required answer is 10/(10+20) = 1/3
_________________
Press +1 Kudos if you find this Post helpful



Manager
Joined: 17 Mar 2015
Posts: 116

Re: Myra drove at an average speed of 30 miles per hour for some time and
[#permalink]
Show Tags
06 Apr 2015, 15:10
I concluded that time could serve as a variable that would let us divide the journey in fractions. Lets same time = 1. X  the fraction. We can then conclude that, since the journey is the same and the total time is the same. \(30*x + 60*(1x) = 50*1\) \(30*x = 10\) \(x = 1/3\) Which means the answer is B



Manager
Joined: 18 Dec 2014
Posts: 99

Re: Myra drove at an average speed of 30 miles per hour for some time and
[#permalink]
Show Tags
07 Apr 2015, 03:30
Average speed of 150:
30 + 60 + 60 = 150 150 / 3 = 50
1 hour of 30 miles an hour 2 hours of 60 miles an hour
30 miles an hour 1/3 of the time.
B.



Math Expert
Joined: 02 Sep 2009
Posts: 52390

Re: Myra drove at an average speed of 30 miles per hour for some time and
[#permalink]
Show Tags
13 Apr 2015, 06:46
Bunuel wrote: Myra drove at an average speed of 30 miles per hour for some time and then at an average speed of 60 miles/hr for the rest of the journey. If she made no stops during the trip and her average speed for the entire journey was 50 miles per hour, for what fraction of the total time did she drive at 30 miles/hour?
(A) 1/5 (B) 1/3 (C) 2/5 (D) 2/3 (E) 3/5
Kudos for a correct solution. VERITAS PREP OFFICIAL SOLUTION:Solution: We know the average speed and must find the fraction of time taken at a particular speed. t1/t2 = (A2 – Aavg)/(Aavg – A1) t1/t2 = (60 – 50)/(50 – 30) = 1/2 So out of a total of 3 parts of the journey time, she drove at 30 mph for 1 part and at 60 mph for 2 parts of the time. Fraction of the total time for which she drove at 30 mph is 1/3. Answer (B)
_________________
New to the Math Forum? Please read this: Ultimate GMAT Quantitative Megathread  All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics



Intern
Joined: 13 Sep 2015
Posts: 17

Myra drove at an average speed of 30 miles per hour for some time and
[#permalink]
Show Tags
07 Nov 2015, 20:40
An alternate approach:
When i cannot figure out a direct way, I try the plug in approach, whcih usually means picking one of the answers and plugging in to your model. I learnt this approach from Princeton Review's Cracking the GMAT which, IMO, is the only saving grace of Princeton Review's book.
fraction of time spent driving at 30 mph= x fraction of time spent driving at 60 mph = y Total time = T d1 = distance travelled at 30 mph d2 = distance travelled at 60 mph
chose 1/3 first because it just felt about right because avg of 50 mph is 20 more than 30mph and 10 less than 60...so I figured the portion of time spent driving at 60 mph should be longer.
which means
x/T = 1/3 (fraction of time spent driving at 30mph) y/T= 2/3 (fraction of time spent driving at 60 mph) Assume T to be 3 hours, then x = 1 hour, y= 2 hours (this works because we just need fraction, not exact or actual time) which would make the distances = d1 = 30 mph x 1 hr = 30 miles d2 = 60 mph x 2 hrs = 120 miles Total distance = 150 miles
finally confirm the answer with, avg speed = total distance/total time = 150/3 = 50 mph
which means 1/3 is correct



VP
Joined: 07 Dec 2014
Posts: 1152

Re: Myra drove at an average speed of 30 miles per hour for some time and
[#permalink]
Show Tags
08 Nov 2015, 12:57
let t=total time x=time @ 30mph d=total distance 30x+60(tx)=d 30x=60td we know that d/50=t ➡ d=50t substituting for d, 30x=10t x/t=1/3



Manager
Joined: 15 Feb 2015
Posts: 100

Re: Myra drove at an average speed of 30 miles per hour for some time and
[#permalink]
Show Tags
24 Nov 2015, 22:58
Bunuel wrote: Myra drove at an average speed of 30 miles per hour for some time and then at an average speed of 60 miles/hr for the rest of the journey. If she made no stops during the trip and her average speed for the entire journey was 50 miles per hour, for what fraction of the total time did she drive at 30 miles/hour?
(A) 1/5 (B) 1/3 (C) 2/5 (D) 2/3 (E) 3/5
Kudos for a correct solution. We don't need to get into calculations for solving this questions. We can use the concept of weighted averages. One thing for sure we know that if the average speed for the entire journey is 50, means she drove at 60mph for a longer duration. 20 10 30 5060 This shows that you can divide the entire journey in 3 parts. Thus, 2/3rd parts she drove at 50 mph and 1/3rd part she drove at 30 mph. Answer: B



Board of Directors
Joined: 17 Jul 2014
Posts: 2598
Location: United States (IL)
Concentration: Finance, Economics
GPA: 3.92
WE: General Management (Transportation)

Re: Myra drove at an average speed of 30 miles per hour for some time and
[#permalink]
Show Tags
12 Feb 2016, 18:23
pretty straight forward question... suppose x is the time she drove for 30 miles/hour. total distance = 30x. suppose t is total time she drove. we have average speed = 50 miles. thus, total distance = 50t. she drove 60 miles/hour at tx time. thus, she drove a distance of 60t60x miles at 60 miles/hour. we know the fact that: 30x+60t60x=50t 10t=30x t=3x. ok, so the total time is 3x. she drove x at 30mph. thus, she must have driven x/3x or 1/3 of her time at 30mph.



Target Test Prep Representative
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 4600
Location: United States (CA)

Re: Myra drove at an average speed of 30 miles per hour for some time and
[#permalink]
Show Tags
09 Nov 2018, 12:19
Bunuel wrote: Myra drove at an average speed of 30 miles per hour for some time and then at an average speed of 60 miles/hr for the rest of the journey. If she made no stops during the trip and her average speed for the entire journey was 50 miles per hour, for what fraction of the total time did she drive at 30 miles/hour?
(A) 1/5 (B) 1/3 (C) 2/5 (D) 2/3 (E) 3/5 We can use the formula of average speed = total distance/total time. We can let x and y be the first and second distances, respectively. 50 = (x + y)/(x/30 + y/60) Multiplying by 60/60, we have: 50 = (60x + 60y)/(2x + y) 50(2x + y) = 60x + 60y 100x + 50y = 60x + 60y 40x = 10y 4x = y Thus, the fraction of the time driving 30 mph was: (x/30)/(x/30 + y/60) Since y = 4x, we have: (x/30)/(x/30 + 4x/60) Multiplying by 60/60, we have: 2x/(2x + 4x) 2x/6x 1/3 Alternate Solution: We can use a weighted average approach to answer this question. Had the average speed been 45 miles per hour, we would know that she traveled an equal amount of time at 30 mph and at 60 mph, since 45 is exactly halfway between 30 and 60. However, since the average speed was 50 miles per hour (which is closer to 60 mph than to 30 mph), we see that she traveled at 60 mph for a longer period of time. We see that 60  50 = 10 and 50  30 = 20, so if we break the trip into 3 segments, she traveled 2 of the 3 segments at 50 and 1 of the 3 segments at 30 mph. Thus, the fraction spent driving 30 mph is 1/3. Answer: B
_________________
Scott WoodburyStewart
Founder and CEO
GMAT Quant SelfStudy Course
500+ lessons 3000+ practice problems 800+ HD solutions




Re: Myra drove at an average speed of 30 miles per hour for some time and &nbs
[#permalink]
09 Nov 2018, 12:19






