Question

At 7 am Joe starts sprinting at 6 miles per hour. At 7:10 am, Ken starts off after him. How fast must Ken run in order to overtake him at 7:30 am?

Answer 1

9 mph

1/3*r = 1/2*6
r = 9

Answer 2

hence for joe:
6t=d (where t is time, and d is distance)
for Ken:
v=d/(20/60)
no we know that after 30 minutes that's when ken is supposed to catch up that joe has already ran a distance of:
6*0.5=d, d=3miles
substitute that back into v=d(3)
then, speed of ken should be =3*3= 9 miles an hour