+1310 In a 10-kilometer race, each runner runs 5 km to point P and returns to the start by the same route. Ian runs 4 kilometers per hour faster than Sean. Ian runs to point P, turns around, and meets Sean 4 km from the start. Assume that Ian and Sean each maintain a constant speed and start at the same time. What is Sean's time, in minutes, for running the 10 kilometers?
+128577 Let R be Sean's speed and let R + 4 be Ian's speed (both in km/hr)
Note that, when Ian meets Sean, he has run 6km and Sean has run 4km. And they each have run the same amount of time.......so we have
D/R = T and
Ian's Time = Sean's Time....so...
6/(R + 4) = 4/R cross-multiply
6R = 4(R + 4)
6R = 4R + 16
2R = 16
R = 8 km per hour...and this is Sean's rate
So, Sean runs the 10km in: ..... 10km/(8km/hr) = 5/4 hrs = 5/4(60m min) = 75 min
+128577 Let R be Sean's speed and let R + 4 be Ian's speed (both in km/hr)
Note that, when Ian meets Sean, he has run 6km and Sean has run 4km. And they each have run the same amount of time.......so we have
D/R = T and
Ian's Time = Sean's Time....so...
6/(R + 4) = 4/R cross-multiply
6R = 4(R + 4)
6R = 4R + 16
2R = 16
R = 8 km per hour...and this is Sean's rate
So, Sean runs the 10km in: ..... 10km/(8km/hr) = 5/4 hrs = 5/4(60m min) = 75 min
