SOLUTION: David left Boston on the Coast to Coast Bike Ride, riding at 20 km/hr. Forty-five minutes later, Kristi rode out of Boston at 25 km/hr. If these speeds stay the same, how far dow

Question 918367: David left Boston on the Coast to Coast Bike Ride, riding at 20 km/hr. Forty-five minutes later, Kristi rode out of Boston at 25 km/hr. If these speeds stay the same, how far down the road will David be when Kristi catches up to him?
Answer by josmiceli(19441) (Show Source): You can put this solution on YOUR website!
David's head start is:
( 45 min = 3/4 hr )
km
--------------------
Start a stopwatch when Kristi leaves
Let = time on the stopwatch in hrs
when she catches David
------------------------
Let = distance in km from Boston when
she catches David
---------------------
David's equation:
(1)
Kristi's equation:
(2)
---------------
Substitute (2) into (1)
(1)
(1)
(1) hrs
and
(2)
(2)
(2) km
----------------
Kristi catches him 75 km from Boston
check:
(1)
(1)
(1)
OK

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