A certain car increased its avarage speed by 5 miles per

Question

A certain car increased its average speed by 5 miles per hour in each successive 5-minute interval after the first interval. If in the first 5-minute interval its average speed was 20 miles per hour, how many miles did the car travel in the third 5-minute interval?

A) 1.0
B) 1.5
C) 2.0
D) 2.5
E) 3.0

A) 1.0
B) 1.5
C) 2.0
D) 2.5
E) 3.0

Bunuel · Accepted Answer

In the third time interval the average speed of the car was 20+5+5=30 miles per hour;
In 5 minutes (1/12 hour) at that speed car would travel 30*1/12=2.5 miles.

Answer: D.

PareshGmat · Answer

Please refer diagram below

Answer = D

M3tm4n · Answer

Damn it. Thanks Bunuel. I calculated the total milage instead of only that of the third segment!! :evil:

Raihanuddin · Answer

Had the question asked, how long did the car travel up to third minute interval, how could we have found the answer. Please explain it.

Bunuel · Answer

I guess you mean the total distance covered in three 5-minute intervals.

The distance covered in the first 5-minute interval = (time)(average speed) = 1/12*20;
The distance covered in the second 5-minute interval = (time)(average speed) = 1/12*25;
The distance covered in the third 5-minute interval = (time)(average speed) = 1/12*30.

Total distance = 1/12(20+25+30) = 75/12 miles.

EMPOWERgmatRichC · Answer

Hi All, Here's a similarly-themed question: the-average-speed-of-a-car-decreased-by-3-miles-per-hour-12994.html#p1520197 GMAT assassins aren't born, they're made, Rich

Nadiuska · Answer

Miles per minute on the third interval: 30/60 =1/2. After 5 minutes=( 1/2)*5= 2.5

PrijitDebnath · Answer

After first 5-minute interval, speed increases to 25 miles per hour
After second 5-minute interval, speed increases to 30 miles per hour
So, in the third 5-minute interval, speed is 30 miles per hour

60 minutes corresponds to 30 miles per hour
So, 5-minutes corresponds to (30/60)*5 = 2.5 miles

dave13 · Answer

I guess you mean the total distance covered in three 5-minute intervals. The distance covered in the first 5-minute interval = (time)(average speed) = 1/12*20; The distance covered in the second 5-minute interval = (time)(average speed) = 1/12*25; The distance covered in the third 5-minute interval = (time)(average speed) = 1/12*30. Total distance = 1/12(20+25+30) = 75/12 miles. Bunuel how did you calculate time ?

1/12 ...does it means that it takes 5 minutes for every 12 miles ?

Bunuel · Answer

5 minutes is 1/12 hour.

dave13 · Answer

hi Bunuel , if i change 5 minutes into 10 minutes interval. so: first interval the speed id 20 km per hour second interval is 30 km per hour third interval is 40 km per hour Speed = \frac{40 km (distance)}{60 minutes (time)} Time in 10-minute interval, means what distance did the car in 10 minute interval at a speed of 40 km per hour. Time = \frac{distance}{speed} Distance = speed * time ---> \frac{40 km (distance)}{60 minutes (time)} * 10 = 6,7 miles Is my understanding correct ? thank you

JeffTargetTestPrep · Answer

The rate of the car in the first interval was 20 mph, in the second it was 25 mph, and in the third it was 30 mph.

Since 5 minutes = 5/60 = 1/12 hour, the distance traveled in the third interval was 30 x 1/12 = 30/12 = 5/2 = 2.5 miles.

Answer: D

pvs29 · Answer

speed = distance * time

speed on 3rd interval = 20+(5+5) = 30

time = speed/distance; (30/60)*5 = 2.5 minutes

pulak1988 · Answer

after the first interval the speed was increased in suucessive intervals. so that should mean the speed was increase on second interval.

so it should be like ----20m/h----l----20m/h---l ----25m/h----l

dont you think?

CEdward · Answer

Unacceptable that this question took me 5.5 minutes.

A certain car increased its average speed by 5 miles per hour in each successive 5-minute interval after the first interval. If in the first 5-minute interval its average speed was 20 miles per hour, how many miles did the car travel in the third 5-minute interval?

A) 1.0
B) 1.5
C) 2.0
D) 2.5
E) 3.0

A) 1.0
B) 1.5
C) 2.0
D) 2.5
E) 3.0

30 miles per hour x 1 hr / 60 minutes = 1 mile / 2 minutes

5 / 2 = 2.5 miles

D.

BLTN · Answer

Dear dave13 you are correct; your inquisitiveness is a good way to elaborate the issue in detail

taking into consideration your precious question in this topic let us rewrite your solution as follows Distance = 40mph * \frac{1}{6} = 6.67 miles. Hope it helps

BrentGMATPrepNow · Answer

Given : A certain car increased its average speed by 5 miles per hour in each successive 5-minute interval after the first interval. In the first 5-minute interval its average speed was 20 miles per hour.
In other words: 
Speed during the FIRST 5-minute interval = 20 mph
Speed during the SECOND 5-minute interval = 25 mph
Speed during the THIRD 5-minute interval =  30  mph

Question : how many miles did the car travel in the third 5-minute interval? 
During the THIRD 5-minute interval, the car traveled for a time of 5 MINUTES and a speed of  30  miles per HOUR

Important: In order to perform a calculation, we need the same units of time. 
So, we can EITHER convert 5  minutes  to 5/60  hours ...
OR convert  30  miles per  hour  to  30/60  miles per  minute

I'll use both conversions separately (to show either conversion will work)

Approach #1  Converting 5  minutes  to 5/60  hours 
Distance = (rate)(time)
= ( 30  miles per  HOUR )(5/60  hours )
= 150/60 miles
= 15/6 miles
= 5/2 miles
= 2.5 miles
 Answer: D

Approach #2  Converting  30  miles per  hour  to  30/60  miles per  minute  
Distance = (rate)(time)
= ( 30/60  miles per  minute )(5  minutes )
= ( 0.5  miles per  minute )(5  minutes )
= 2.5 miles
 Answer: D

rreda · Answer

In the third 5 minute interval the speed of the car would be 30mph (20+5+5) so the speed would be 30miles/60 minutes or in other words 0,5mph 
so in 5minutes the car would cover 2,5miles
Correct Answer is D. Hope it's clear

Kimberly77 · Answer

Hi  BrentGMATPrepNow , Speed during the THIRD 5-minute interval =  30  mph. Not sure why is the time is not 15 min here in THIRD 5-minute interval according to the question of "in each successive 5-minute interval after the first interval" ? Thanks Brent

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