Question 985243
the sum of the speed of two trains is 719.5 miles per hour 

{{{s[1]+s[2]=719.5 (mil/h)}}}...........eq.1

if the speed of the first train is {{{2.5}}} miles faster than the second train, then we have 
{{{s[1]=s[2]+2(mil/h)}}}.........substitute in eq.1

{{{s[2]+2(mil/h)+s[2]=719.5 (mil/h)}}}.........solve for {{{s[2]}}}

{{{2s[2]=719.5 (mil/h)-2(mil/h)}}}

{{{2s[2]=717.5 (mil/h)}}}

{{{s[2]=(717.5/2) (mil/h)}}}

{{{highlight(s[2]=358.75(mil/h))}}}-the speeds of second train 

and
{{{s[1]=s[2]+2(mil/h)}}}

{{{s[1]=358.75(mil/h)+2(mil/h)}}}

{{{highlight(s[1]=360.75(mil/h))}}}-the speeds of first train 

check the sum:


{{{s[1]+s[2]=719.5 (mil/h)}}}

{{{360.75(mil/h)+358.75(mil/h)=719.5 (mil/h)}}}

{{{719.5(mil/h)=719.5 (mil/h)}}}