SOLUTION: Tina is training for a biathlon. To train for the running portion of the race, she runs 7 miles each day over the same course. The first 4 miles of the course is on level ground, w

Question 1055874: Tina is training for a biathlon. To train for the running portion of the race, she runs 7 miles each day over the same course. The first 4 miles of the course is on level ground, while the last 3 miles is downhill. She runs 3 miles per hour slower on level ground than she runs downhill. If the complete course takes 1 hour, how fast does she run on the downhill part of the course?
Answer by josmiceli(19441) (Show Source): You can put this solution on YOUR website!
Let = time in hrs to run on the downhill part
= time in hrs to run on level ground
= speed in mi/hr running downhill
= speed in mi/hr running on level ground
------------------------------------------------
Equation for funning on level ground:
(1)
Equation for running downhill:
(2)
-----------------------------
(2)
Plug (2) into (1)
(1)
(1)
(1)
Multiply both sides by
(1)
(1)
(1) ( by looking at it )
I have to choose between
and

it can't be since
= speed in mi/hr running on level ground
and I would end up with negative speed
So,
-------------------------------------
She runs 9 mi/hr on the downhill part
-------------------------------------
check:
(2)
(2)
(2)
and
(1)
(1)
(1)
(1)
(1)
(1)
(1)
OK

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