Denise has 5 hours to spend training for an upcoming race. She completes her training by running full speed the distance of the
race and walking back the same distance to cool down. If she runs at a speed of 9mph and walks back at a speed of 3mph, how long should she plan to spend walking back?
<span>To solve this problem, we can use this formula d = rd (distance = rates x time)
She runs at a speed of 9 mph and walks at a speed of 3 mph.
Her distance running is
d = 9tr
where tr is the time she spends running
Her distance walking is
d = 3tw
where tw is the time she spends walking
The distances are the same so
9tr = 3tw
We also know that the total time is 5 hours
tr + tw = 5
tr = 5-tw
Substitute this value of tr in the first equation
9tr = 3tw
9(5-tw) = 3tw
45-9tw = 3tw
45 = 12tw
3.75= tw
Denise will spend 3.75 hours (3 hours, 45 minutes) walking back and 1.25 hours (1 hour, 15 minutes) running.</span>
