A bike rider went up a hill at 10 mph and back down the same route at 20 mph. what is his average speed on the whole trip?
2007-09-29 08:52:30 · 19 answers · asked by Cerina A 3 in Science & Mathematics ➔ Mathematics
When calculating average speeds, people often commit the mistake of averaging actual speeds. This does not work because when speed is higher, the same distance is covered in a lesser time. The correct way is to find the total distance traveled and then the time it took to travel that distance and then compute the average speed using the formula: speed=(distance/time).
Let us do this for this problem. Suppose the distance from the base of the till to the top of the hill is x miles.
Time taken for uphill ride (t1) = x/10
Time taken for downhill ride (t2) = x/20
Total time taken (t1+t2) = 3x/20
Total distance covered = 2x miles
Average speed = 2x/(3x/20) = 40/3 = 13.3333..miles per hour. This is the correct answer.
In this problem, if the bike rider rides for equal time with two different speeds, instead of equal distance, then you can calculate the average speed as some of the people have done here - You can just add up the speeds and divide by 2. Then the answer would have been 15 miles per hour.
2007-09-29 09:17:13 · answer #1 · answered by Prakash D 2 · 0⤊ 0⤋
Wow I am amazed at how every answer on here is wrong.
Look, average speed is Distance divided by Time.
A rider went up a hill at 10 mph and back down the same hill (distance) at 20 mph.
Therefore he was traveling at 10 mph for a time x and 20 mph for half of time x. Therefore of the whole time 1.5x, he was traveling 10 mph for 2/3 of that time and 20 mph for 1/3 of that time. So the answer is 13 1/3 mph.
Edit: Sorry I now see some correct answers, there were none though when I was typing it.
2007-09-29 09:07:32 · answer #2 · answered by John L 2 · 0⤊ 0⤋
There is a route up the hill and a route down the hill. That is two trips . . .
You would add 10 mph and 20 mph (the total average speed of the trip) and divide by 2 (two trips)
(10 + 20)/2 = 15 mph
2007-09-29 08:57:13 · answer #3 · answered by Tina R 4 · 1⤊ 2⤋
U have to add 20+10=30 then divide 30/2 and u get 15 mph
2007-09-29 09:04:09 · answer #4 · answered by JB♥ 2 · 0⤊ 1⤋
Average speed would require us to know the distance he travelled.
If the ride at 10 mph was the same distance as the ride at 20 mph, then the average is the 2 values added together and the total divided by 2, or (10 + 20)/2 = 15 mph.
But if he rode farther at 10 mph than he rode at 20 mph, his average speed would be less than that.
2007-09-29 08:56:29 · answer #5 · answered by Anonymous · 1⤊ 2⤋
Your average speed is the total distance divided by the total time. Let's assume the hill is 10 miles.
going up: 10 miles at 10mph= 2 hour
going down: 10 miles at 20mph= 1 hour
Total distance=20 miles
Total time=1.5 hours
So, 20 miles / 1.5 hours = 13.33333 mph
Try this out using different miles to test.
2007-09-29 09:00:34 · answer #6 · answered by Ziggy 3 · 0⤊ 0⤋
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2016-12-17 13:01:35 · answer #7 · answered by trickey 4 · 0⤊ 0⤋
15
2007-09-29 08:56:13 · answer #8 · answered by jive987 2 · 0⤊ 2⤋
ok to find the average speed all you have to do is add 20+10 and then divide the answer by two and you will get your answer of 15mph!! 20+10=30
30/2=15 and thats all you do
2007-09-29 08:59:07 · answer #9 · answered by Anonymous · 0⤊ 1⤋
15 mph
2007-09-29 08:55:14 · answer #10 · answered by CW 3 · 0⤊ 2⤋