Question 1077949
 a boat travels 70 miles and then comes back, the current was 20 mph the total trip time was 4 hours and 40 minutes, how fast was the boat traveling
<pre>Let boat's speed be S
Then we get the following TIME equation: {{{matrix(1,3, 70/(S - 20) + 70/(S + 20), "=", 4& 40/60)}}}_____{{{matrix(1,3, 70/(S - 20) + 70/(S + 20), "=", 14/3)}}}
70(3)(S + 20) + 70(3)(S - 20) = 14(S - 20)(S + 20) -------- Multiplying by LCD, 3(S - 20)(S + 20)
{{{210S + 210(20) + 210S - 210(20) = 14S^2 - 14(400)}}}
{{{420S = 14S^2 - 14(400)}}}
{{{14S^2 - 420S - 14(400) = 0}}}
{{{14S^2 - 420S - "5,600" = 0}}}
{{{14(S^2 - 30S - 400) = 14(0)}}}
{{{S^2 - 30S - 400 = 0}}}
(S - 40)(S + 10) = 0
S, or boat's speed = {{{highlight_green(matrix(1,2, 40, mph))}}}          OR         S = - 10 (ignore)