fiendex wrote:
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
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
hoursDistance = (rate)(time)
= (
30 miles per
HOUR)(5/60
hours)
= 150/60 miles
= 15/6 miles
= 5/2 miles
= 2.5 miles
Answer: DApproach #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