Question 120632
I need to use {{{d = r*t}}}. There is a separate equation for
bike and car
{{{d[b] = r[b]*t[b]}}}
{{{d[c] = r[c]*t[c]}}}
Call the distance the car travels {{{d[b] + 60}}} km
Then the distance the bike travels is {{{d[b]}}} km
Given: {{{r[c] = 4*r[b]}}}
We are starting a stopwatch at noon and stopping it at 1:00 PM, so
{{{t[b] = 1}}} hr
{{{t[c] = 1}}} hr
{{{d[b] = r[b]*1}}}
{{{d[b] + 60 = 4*r[b]*1}}}
substitute {{{r[b]*1}}} for {{{d[b]}}} in the 2nd equation
{{{r[b] + 60 = 4*r[b]}}}
{{{3*r[b] = 60}}}
{{{r[b] = 20}}} km/hr answer
{{{r[c] = 4*20}}}
{{{r[c] = 80}}} km/hr answer
check
{{{d[b] = r[b]*t[b]}}}
{{{d[c] = r[c]*t[c]}}}
----------------------
{{{d[b] = 20*1}}}
{{{d[c] = 80*1}}}
The difference is 60 km
OK