A certain car increased its avarage speed by 5 miles per

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

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.

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.

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

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

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

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.[/quote]

Bunuel how did you calculate time ? 1/12 ...does it means that it takes 5 minutes for every 12 miles ?

5 minutes is 1/12 hour.

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

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

speed = distance * time

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

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

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?

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

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

5 / 2 = 2.5 miles

D.

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

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

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

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