Question 1197435

plese help me in my homework thankyousomuch!!
car at a certain speed travels 120km during the first part. On the second part, it reduces its speed by 10kph when it travels 100km.find the speed on each part of the trip in the trip lasted for 4hours
<pre>Let average speed during 1st part be S
Then average speed during 2nd part = S - 10
With 1st-leg distance being 120 km, time taken to complete 1st leg = {{{120/S}}}
With 2nd-leg distance being 100 km, time taken to complete 2nd leg = {{{100/(S - 10)}}}
We then get the following TIME equation: {{{matrix(1,3, 4, "=", 120/S + 100/(S - 10))}}}
                                         {{{matrix(1,3, 1, "=", 30/S + 25/(S - 10))}}} ----- Factoring out GCF, 4, in numerator
                                  S(S - 10) = 30(S - 10) + 25S ----- Multiplying by LCD, S(S - 10)
                         {{{matrix(3,3, S^2 - 10S, "=", 30S - 300 + 25S, S^2 - 10S - 55S + 300, "=", 0, S^2 - 65S + 300, "=", 0)}}}
                            (S - 60)(S - 5) = 0
   <font color = red><font size = 4><b>Average speed during 1st leg</font></font></b>, or S = <font color = red><font size = 4><b>60 km/h</font></font></b>      or       S = 5 km/h (ignore)
         
         <font color = red><font size = 4><b>Average speed during 2nd leg</font></font></b> = <font color = red><font size = 4><b>60 - 10 = 50 km/h</font></font></b></pre>