Question 306365
Ave speed  = (total distance)/(total time)
Let {{{d}}} = distance to city
Let {{{s}}} = his returning speed
given:
{{{d/50}}} = time to get to city
{{{(d + d)/(d/50 + d/s) = 60}}}
{{{2d = 60*(d/50 + d/s)}}}
{{{2d = 60d(1/50 + 1/s)}}}
{{{1/30 = 1/50 + 1/s}}}
Multiply both sides by {{{150s}}}
{{{5s = 3s + 150}}}
{{{2s = 150}}}
{{{s = 75}}}
His return speed was 75 mi/hr