Question 956621
If I need to drive 120 km in 120 minutes, and for the first half an hour travel at 70km/h, how fast will I have to travel to make it on time?
:
Let s = the speed required on the remaining part of the trip in 90 min (1.5 hrs)
Find the distance traveled in 1/2 hr at 70 mph
{{{1/2}}} * 70 = 35 mi
Find the distance traveled at some other speed
120 - 35 = 85 km
Find the speed you have to drive to travel 85 km in 1.5 hrs
{{{85/s}}} = 1.5
1.5s = 85
 s = 85/1.5
 s = 56{{{2/3}}} km/hr