David Gwyn J. answered • 10/29/20

Oxbridge grad w/ PGCE in Mathematics & 10+ yrs of teaching experience

speed/distance/time equation **s = d/t (or t = d/s or d = st)...**

x mph = x/60 mpmin (e.g. 6 mph = 0.1 mpmin)

60 minutes total

-10 minutes in store = 50 minutes

running speed = 2x walking speed, and same distance there & back, so 2/3 time walking (2/3 x 50) and 1/3 time running (1/3 x 50)

d = st = 6/60 x 50/3 = 1/10 x 50/3 = 1 x 5/3 = **1 **^{2}**/**_{3}** miles from store**

(or d = st = 3/60 x 100/3 = 1/20 x 100/3 = 1 x 5/3 = 1 2/3 miles from store)

to check... 5/3 miles from store... run at 6mph = 5/18 of hour

5/3 miles from store... walk at 3mph = 5/9 of hour

5/9 + 5/18 = 15/18 hour

15/18 x 60 = 50 minutes