SOLUTION: Dora drove east at a constant rate of 75 kph. One hour later, Tim started driving on the same road at a constant rate of 90 kph. For how long was Tim driving, before he caught up t

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Question 917069: Dora drove east at a constant rate of 75 kph. One hour later, Tim started driving on the same road at a constant rate of 90 kph. For how long was Tim driving, before he caught up to Dora?
I have tried to use a table
i set it up like this
Name|D(mi)|R(kph)|T(hr.)|
Dora| d |75 |t |
Tim | d |90 |t+1 |
and then I went and i tried to put it into an equation
75t=90(t+2)
75t=90t+180
-90t -90t
-15t=180
____ ____
-15 -15
t=-12
but It is not an answer on my multiple choice and it wouldn't be a negative 12 hours
-15
Found 2 solutions by josgarithmetic, MathTherapy:
Answer by josgarithmetic(39620)   (Show Source): You can put this solution on YOUR website!
RT=D rate time distance, uniform rates rule for travel
Let t be amount of time Tim drove to catchup to Dora;
Let d be the distance that both Tim and Dora traveled when Tim reaches Dora.

______________________speed________time________distance
Dora___________________75__________t+1__________d
Tim____________________90___________t___________d

The use of this travel uniform rates rule gives and . Both are formula for the same distance, d.


Answer by MathTherapy(10553)   (Show Source): You can put this solution on YOUR website!

Dora drove east at a constant rate of 75 kph. One hour later, Tim started driving on the same road at a constant rate of 90 kph. For how long was Tim driving, before he caught up to Dora?
I have tried to use a table
i set it up like this
Name|D(mi)|R(kph)|T(hr.)|
Dora| d |75 |t |
Tim | d |90 |t+1 |
and then I went and i tried to put it into an equation
75t=90(t+2)
75t=90t+180
-90t -90t
-15t=180
____ ____
-15 -15
t=-12
but It is not an answer on my multiple choice and it wouldn't be a negative 12 hours
-15 


You should let time that it takes Tim to catch up to Dora be T

Since Dora will take a longer time as she's travelling at a slower rate of speed than Tim, time she'll take is: T + 1

Thus, your equation is: 90T = 75(T + 1)

Solve for T, the time Tim will take. 

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