Question 166763
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Working Eqn ----> {{{Speed=Distance/time}}}
Conditions:
Speed of Jeff: {{{S[jf]=x+15}}}, 15mph faster than brother
Speed of brother: {{{S[br]=x}}}
Distance covered by Jeff in {{{t[jf]=3hours}}}: {{{D[jf]=2*D[br]}}}, twice that of brother covered in {{{t[br]=4hours}}}
Via Working eqn,
{{{D=(Speed)(time)}}}
We equate the 2 distances by both:
{{{D[jf]=2D[br]}}}
{{{(S[jf])(t[jf])=2((S[br])(t[br]))}}}
{{{(x+15)(3hrs)=2((x)(4hrs))}}}
{{{3x+45=8x}}} 
{{{45=8x-3x=5x}}} ----> {{{cross(45)9/cross(5)=cross(5)x/cross(5)}}}
{{{highlight(x=9mph)}}}, Speed of brother
{{{9+15=highlight(24mph)}}}, Speed of Jeff
In doubt? Let's check their distance, via working eqn,
Distance covered by Jeff is twice as much ----> {{{D[jf]=(24)(3)=72miles}}}
{{{D[br]=(9)(4)=36miles)}}}
Thank you,
Jojo</pre>