Ok here it goes...
Maria covered the first half of a bicycle race at 20 miles per hour. The second half of the race was a return over the same route, and her return was 30 miles per hour. What was Maria's average speed for theentire trip. Take your time with this.
2007-04-27 18:07:40 · 9 answers · asked by Anonymous in Science & Mathematics ➔ Mathematics
distance=rate * time
if x is the distance travelled one way then 2x is total distance.
The first half, the time is x/20 and the second half time is x/30
So, the average rate=2x/(x/20+x/30) = 2x(5x/60)=120/5=24
The average speed is 24 mph
2007-04-27 18:18:23 · answer #1 · answered by Anonymous · 1⤊ 0⤋
Distance of race = 2x miles
x miles at 20 miles an hour takes x/20 hours
x miles at 30 miles an hour takes x/30 hours
Total time taken = x/20 + x/30 =5x/60 = x/12 hours
Average speed = distance / time = 2x/(x/12) = 24 miles per hour
2007-04-27 18:18:25 · answer #2 · answered by gudspeling 7 · 0⤊ 0⤋
Let say the x is the distance for the first half of the race, y1 is the time needed for Maria to finish the first half of the race and y2 is the time needed for Maria to finish the second half of the race.
Therefore the distance of the race is 2 times x. Distance of the first half of the race is 20 times y1 and the second half of the race is 30 times y2. Since the distance is the same, therefore y1+y2 times 50 is the total distance.
Average speed is calculated by the total distance divided by the total time used. The total time used is y1+y2. Therefore, (y1+y2)(50)/(y1+y2). The answer will be 50 miles per hour.
2007-04-27 19:29:11 · answer #3 · answered by cheezz 2 · 0⤊ 1⤋
You don't need help for such an averaging problem. Sum the total distance. Divide by the total time it took to cover the distance. Since the distance is the same both ways, forget time. Just sum and divide by two. That's plenty close enough for most cases.
Let's get closer:
The total time is (miles/speed + miles/speed).
total time is (x/20 + x/30) = x * (1/20+1/30) That's about x* (0.0833) Now the average speed is given by total distance divided by time. 2 * x divided by (x * 0.0833) is about 24 miles per hour.
I still think 25 is close enough.
2007-04-27 18:19:55 · answer #4 · answered by Jack 7 · 0⤊ 1⤋
average speed = total distance/total time
total distance = 2d
time1 = d/20
time2 = d/30
average speed = 2d/(d/20 + d/30)
= 2/(1/20 + 1/30) = 2*60/(3 + 2)
= 120/5 = 24 mph
2007-04-27 19:10:51 · answer #5 · answered by sweetwater 7 · 0⤊ 0⤋
25 miles per hour
2007-04-27 18:19:53 · answer #6 · answered by Arizona Chick 5 · 0⤊ 0⤋
25 mph. duh.
you only have to do any REAL math if you're looking for time AND speed.
there's nothing more you can do with such little information.
that's the answer.
2007-04-27 18:13:28 · answer #7 · answered by sahariah 3 · 0⤊ 3⤋
the answer is 24m/ h .right?
2007-04-27 18:14:55 · answer #8 · answered by Anonymous · 1⤊ 0⤋
25
duh!
2007-04-27 18:46:01 · answer #9 · answered by Anonymous · 0⤊ 0⤋