Expert: Ahmed Salami - 12/12/2005

Question
It takes 24 minutes to complete a 5-kilometer race. What is the runner speed in miles per hour?Round to the tenths palce note 1km=0.621 mi and 1 hr=6

Answer
Hi Natalie,
Distance = 5km
Time = 24 mins
speed = distance/time
so we can simply say
speed = (5/24)(km/mins)
But 1km = 0.621miles and 1min = (1/60)hr
Replacing gives
speed = (5/24)(0.621miles)/(1/60)hr
     = (5/24)(0.621miles)60/hr
     = (5/24)(0.621)(60)(miles/hr)
     = 7.7625 miles/hr
     = 7.8 miles/hr to the tenths place
Or if that is tedious to you, why not say
5km = 5(0.621) miles
24 min = (24/60) hr
Therefore,
speed = 5(0.621)/ (24/60) miles/hr
and you'll still have the same result.
Sorry for the time taken.
I hope it is clear, you can always get back to me.
Regards.