Problema Solution
Janelle has three hours to spend training for a race. She completes her training by running full speed the distance of the race and walking back to cool down. If she runs at a speed of 10 miles per hour and walks back at a speed of two miles per hour, how long should she spend walking back?
Answer provided by our tutors
Let
v1 = 10 miles per hour be Janelle's ruining speed
v2 = 2 miles per hour be Janelle's walking back speed
t1 = the time she spends completing the race
t2 = the time she spends walking back
We need to find t2. Then we can write down this equations
t1 + t2 = 3 (Janelle has three hours to spend training for a race)
v1*t1 = v2*t2 ( the distance she runs equals the distance she walks back)
That is we have the following system
t1 + t2 = 3
10*t1 = 2*t2
the solutions of the system are
t1 = 0.5 hours
t2 = 2.5 hour = 2 hours 30 min
Janelle spends 2 hours 30 min walking back.