Question 975161

let actual speed be {{{s}}}
if a car traveling with {{{5/7}}} of its actual speed,we have  {{{(5/7)s}}}

if a car covers a distance {{{d=42km}}} in a time {{{t=1h}}}{{{ 40min}}}{{{48s}}}, then we have

{{{d=s*t}}}

{{{42km=(5/7)s*t}}}

....convert time to hours: 
{{{1h  = 1h}}}
{{{40min = 40/60 = (2/3)h}}}
{{{48s = 48/3600 = (1/75) h}}}

Therefore, 1 hr 40 min 48 sec = 1 + 2/3 + 1/75 hour = 126/75 hour

{{{t=1h}}}{{{ 40min}}}{{{48s}}}={{{(1 + 2/3 + 1/75 )h = (126/75) h=1.68h}}}

{{{42km=(5/7)s*1.68h}}}

{{{42km/1.68h=(5/7)s}}}

{{{4200km/168h=(5/7)s}}}

{{{25(km/h)=(5/7)s}}}

{{{(7*25/5)(km/h)=s}}}

{{{(7*cross(25)5/cross(5)1)(km/h)=s}}}

{{{(7*5)(km/h)=s}}}

{{{s=35(km/h)}}}