SOLUTION: You are walking across a rail bridge, and are 3/8 of the way across.
You hear a train approaching behind you at 60 miles per hour.
You do some quick calculation,
Algebra.Com
Question 204382: You are walking across a rail bridge, and are 3/8 of the way across.
You hear a train approaching behind you at 60 miles per hour.
You do some quick calculation, and you realize that you can either run back or forward, and either way, you can make it to the end of the bridge and get off the tracks, just in time to avoid getting hit by the train. That is, you will get to the end of the bridge (either behind you or in front of you) the exact same time as the train.
What is your running speed?
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
:
You are walking across a rail bridge, and are 3/8 of the way across.
You hear a train approaching behind you at 60 miles per hour.
You do some quick calculation, and you realize that you can either run back
or forward, and either way, you can make it to the end of the bridge and get
off the tracks, just in time to avoid getting hit by the train.
That is, you will get to the end of the bridge (either behind you or in front
of you) the exact same time as the train.
What is your running speed?
:
Train----------d------------Br.....3x......Y..........5x.........Br
:
Let d = dist train is from the bridge
Let 8x = length of the bridge
You (Y) are 3x from one end and 5x from the other end of the bridge
:
Let s = running speed (mph)
:
Toward the train time equation (arrive at end of the bridge at the same time)
Train time = your time
=
Cross multiply:
ds = 60(3x)
ds = 180x
d =
:
Away from the train time equation (arrive at other end at the same time)
=
Cross multiply
s(d+8x) = 60(5x)
s(d+8x) = 300x
d + 8x =
Replace d with (from the 1st equation)
+ 8x =
Get rid of x, divide thru by x and you have:
+ 8 =
Multiply by s:
180 + 8s = 300
8s = 300 - 180
8s = 120
s =
s = 15 mph running speed
:
:
RELATED QUESTIONS
A man is pedaling his bike across a narrow bridge when he hears a train approaching from... (answered by ankor@dixie-net.com)
Mike was racing in a bike marathon. He was 3/8 of the way across a narrow bridge when he... (answered by ankor@dixie-net.com)
A man is 2/5 the way walking accross a railroad bridge whenhe hears a train approaching... (answered by Paul)
A man is walking on a railroad bridge that goes from A to B. When he is 3/8 the way... (answered by richwmiller)
Two people were crossing a bridge together and were 3/8 across the bridge when they saw a (answered by ankor@dixie-net.com)
A man is three eighths of the way across a bridge when he hears a train coming from... (answered by KMST)
The boys were 3/8 of the way across a bridge when they heard the Cannonball Express... (answered by ankor@dixie-net.com)
A man is three eighths of the way across a train bridge when he hears a train coming from (answered by ankor@dixie-net.com)
Kids are one third the way across a bridge when they hear the sound of a train whistle.... (answered by ankor@dixie-net.com)