Question 147179
Assume I have a stopwatch and I'm on train b
I'm in contact by cellphone with the station
They tell me that train a went by at 12:10.
Then I pass the station at 12:22, and I start my stopwatch
{{{12}}} minutes went by, or {{{12/60}}} hr
I know that train a travels at 60 mi/hr
{{{d = r*t}}}
{{{d = 60*(12/60)}}}
{{{d = 12}}}mi
That's how far train a has gone ahead of me
I'm going to press the stopwatch again when the trains meet.
Let {{{d}}}= the distance I (train b) will have gone in that time
Then {{{d - 12}}} will be the distance that train a has gone.
I can write
{{{d - 12 = 60t}}}
{{{d = 70t}}}
Substitute the 2nd equation in the 1st
{{{70t - 12 = 60t}}}
{{{10t = 12}}}
{{{t = 1.2}}} hr
or 1 hr 12 min
This is 1 hr 12 min past 12:22 when I started the stopwatch, or
13:34, which is 1:34 PM