SOLUTION: Two cargo trains leave the train depot at the same time and are going in the same direction. One travels at 60 miles per hour, and the other travels at 45 miles per hour. Which sys

Question 66941: Two cargo trains leave the train depot at the same time and are going in the same direction. One travels at 60 miles per hour, and the other travels at 45 miles per hour. Which system of equations could you use to find how long it will take for the trains to be 75 miles apart?
Answer Choices:
A) t=45d
t=60(d+75)
B) d=45t
d+75=60t
C) d=45t-75
d=60t
D) d=45(t+75)
d=60t
Answer by ptaylor(2198) (Show Source): You can put this solution on YOUR website!
Two cargo trains leave the train depot at the same time and are going in the same direction. One travels at 60 miles per hour, and the other travels at 45 miles per hour. Which system of equations could you use to find how long it will take for the trains to be 75 miles apart? \
Let t= time it takes for the trains to be 75 mi apart
For the 60 mph train: d1=60t
For the 45 mph train d2=45t
d1-d2=75 mi
60t-45t=75
15t=75
t=5 hours
AND THE ANSWER ABOVE IS B; SUBSTITUTE d=45t INTO THE OTHER EQUATION:

ck
In 5 hours the 60 mph train has travelled 300 mi
In 5 hours the 45 mph train has travelled 225 mi
300-225=75 mi

Hope this helps------ptaylor
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