Question 447136: "C leaves from home going 40 kilometers per hour (km/h). When C is 9 km from home, D starts after C from the same place, going 58 km/h. How long does it take for D to catch up with C?"
I know the formula is "d=r*t", but other than that I'm confused.
Found 2 solutions by richard1234, scott8148:
Answer by richard1234(7193)   (Show Source):
You can put this solution on YOUR website! You could use D = rt on each person, but the faster way is to note the difference in the speeds.
Since D is going 18 km/h faster than C, then relative to C, D is moving at 18 km/h. They are originally 9 km apart, so
9 km = (18 km/h)t --> t = 1/2 hr = 30 minutes.
(Note that when we used relative speeds, we were allowed to assume that C is stationary and D is moving at 18 km/h).
Answer by scott8148(6628)  (Show Source):
You can put this solution on YOUR website! a lot of info given, but just look at it logically
C has a 9 km head start
___ and D is catching up at 18 km/h (58 - 40)
so, how long to close the 9 km gap
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