Question 1092089

Jane took 15 min to drive her boat upstream to water-ski at her favorite spot. Coming back later in the day, at the same boat speed took her 10 min. If the current in that part of the river is 4 km per hr, what was her boat speed in still water?
<pre>Let sped in still water be S
Then we get the following DISTANCE equation: {{{(15/60)(S - 4) = (10/60)(S + 4)}}}
{{{(1/4)(S - 4) = (1/6)(S + 4)}}}
{{{(S - 4)/4 = (S + 4)/6}}}
6(S - 4) = 4(S + 4) ------- Cross-multiplying 
6S - 24 = 4S + 16
6S - 4S = 16 + 24
2S = 40
S, or speed in still water = {{{highlight_green(matrix(1,4, 40/2, "=", 20, "km/h"))}}}
IGNORE anyone who says otherwise!