Nina and Jo both ran a 9 km race. Nina took 1 hour 15 minutes to run the whole race.
Jo started the race 4 minutes later than Nina but caught up when they had both travelled 6 km.
If Nina and Jo both ran at constant speeds, what is Jo's speed to 2 dp?

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  7.83 km/h

Step-by-step explanation:

At her constant pace, Nina's time for 6 km will be found by the proportion ...

  (time for 6 km)/(6 km) = (time for 9 km)/(9 km)

  time for 6 km = (6 km)/(9 km) × (75 min) = 50 min

Jo's time for the same distance will be 4 minutes less: 50 -4 = 46 min. Jo's speed is ...

  speed = distance/time

  = (6 km)/(46/60 h) = 360/46 h ≈ 7.83 km/h . . . . Jo's speed

Additional comment

From the 6 km point, the remaining race is half the distance already run, so will take half the time already taken. As we know, Nina will finish in 25 more minutes; Jo will finish in 46/2 = 23 more minutes, 2 minutes ahead of Nina.

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step-by-step explanation: