GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 21 Jan 2019, 14:15

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

## Events & Promotions

###### Events & Promotions in January
PrevNext
SuMoTuWeThFrSa
303112345
6789101112
13141516171819
20212223242526
272829303112
Open Detailed Calendar
• ### GMAT Club Tests are Free & Open for Martin Luther King Jr.'s Birthday!

January 21, 2019

January 21, 2019

10:00 PM PST

11:00 PM PST

Mark your calendars - All GMAT Club Tests are free and open January 21st for celebrate Martin Luther King Jr.'s Birthday.
• ### The winners of the GMAT game show

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.

# Brian drives a certain part of his journey at an average speed of 30 m

Author Message
Senior DS Moderator
Joined: 27 Oct 2017
Posts: 1199
Location: India
GPA: 3.64
WE: Business Development (Energy and Utilities)
Brian drives a certain part of his journey at an average speed of 30 m  [#permalink]

### Show Tags

15 Jul 2018, 08:58
1
00:00

Difficulty:

55% (hard)

Question Stats:

50% (01:48) correct 50% (02:26) wrong based on 16 sessions

### HideShow timer Statistics

Brian drives a certain part of his journey at an average speed of 30 miles per hour and the rest at an average speed of 60 miles per hour. If he drives for 100 miles, is his average speed for the journey greater than 45 miles per hour?

(1) Brian drives for 30 miles per hour for twice the time than he drives for 60 miles per hour.

(2) Had Brian driven at an average speed of 40 miles per hour rather than 30 miles per hour, his average speed for the journey would have been 48 miles per hour.

_________________
Math Expert
Joined: 02 Aug 2009
Posts: 7212
Re: Brian drives a certain part of his journey at an average speed of 30 m  [#permalink]

### Show Tags

15 Jul 2018, 10:25
Brian drives a certain part of his journey at an average speed of 30 miles per hour and the rest at an average speed of 60 miles per hour. If he drives for 100 miles, is his average speed for the journey greater than 45 miles per hour?

(1) Brian drives for 30 miles per hour for twice the time than he drives for 60 miles per hour.
This means he travels equal distance at both 30mph and 60mph..
So total time taken = 50/30+50/60=150/60=5/2..
AVG speed = 100/(5/2)=200/5=40mph
Sufficient to say NO

(2) Had Brian driven at an average speed of 40 miles per hour rather than 30 miles per hour, his average speed for the journey would have been 48 miles per hour.
Let x be at 60mph
So (X/60)+(100-x)/40=(2x+300-3x)/120=(300-x)/120
AVG speed =100/(300-x)/120=100*120/(300-x)=48..
300-x=100*120/48=250.......X=300-250=50
Now we know miles traveled at 60mph is 50 and remaining 50 is at 30mph..
Sufficient

D

Of course we don't require to solve for the answer the moment we know we can get one solution
_________________

1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html

GMAT online Tutor

Senior DS Moderator
Joined: 27 Oct 2017
Posts: 1199
Location: India
GPA: 3.64
WE: Business Development (Energy and Utilities)
Re: Brian drives a certain part of his journey at an average speed of 30 m  [#permalink]

### Show Tags

16 Jul 2018, 07:07
(1) Brian drives for 30 miles per hour for twice the time than he drives for 60 miles per hour.
Let Brian drives for t hour at speed of 60, and 2t at speed of 30
Total distance = t*60+ 2t*30 = 120t
total time taken = t+2t = 3t
Average speed = 120t/3t = 40, sufficient to answer.

(2) Had Brian driven at an average speed of 40 miles per hour rather than 30 miles per hour, his average speed for the journey would have been 48 miles per hour.

if 40 and 60 gives Avg speed = 48. that means driving time at 40 speed is more than driving time at 60 ( using alligation principle),
Hence we get that in actual driving time at 30 is more than 60 in real question hence the avg speed is less than average of 30 & 60 ie. 45
hence it is sufficient to say that average speed is less than 45 miles per hour.

Sufficient.

Attachments

WhatsApp Image 2018-07-16 at 20.31.22.jpeg [ 40.21 KiB | Viewed 125 times ]

_________________
Re: Brian drives a certain part of his journey at an average speed of 30 m &nbs [#permalink] 16 Jul 2018, 07:07
Display posts from previous: Sort by