Question 1163114

Jennifer drove 300 miles to see her friend. On the return trip, she drove 10 mph faster, so she made the return trip in 1 hour less time. What was her speed on the way to friend's home.
<pre>Let speed on outbound leg be S
Then speed on return leg = S + 10
We then get the following TIME equation: {{{matrix(1,3, 300/S, "=", 300/(S + 10) + 1)}}} 
300(S + 10) = 300S + S(S + 10) ------ Multiplying by LCD, S(S + 10)
{{{matrix(3,3, 300S + "3,000", ""="", 300S + S^2 + 10S, 0, ""="", S^2 + 10S + 300S - 300S - "3,000", 0, ""="", S^2 + 10S - "3,000"))}}}
0 = (S - 50)(S + 60)
S - 50 = 0           OR           S + 60 = 0
Speed on outbound leg, or {{{highlight_green(matrix(1,4, S, "=", 50, mph))}}}  OR     S = - 60 (ignore)