SOLUTION: A boat traveled downstream a distance of 48 miles and then came right back. If the speed of the current was 12 mph and the total trip took 5 hours and 20 mins, find the average spe

The unknown variable is r, and the other variables are for given values.

            SPEED       TIME         DISTANCE

DOWNST      r+c         d/(r+c)       d

UPSTR       r-c         d/(r-c)       d

TOTAL                    t

Bemow you'll find the correct setup and CORRECT answer. 

Let boat's average speed be S

Then the time gong downstream = , and time spent going upstream = 

We get the following TIME equation: 

                                     ---- Factoring out GCF, 16, in numerator

                                    3(3)(S - 12) + 3(3)(S + 12) = (S + 12)(S - 12) ------ Multiplying by LCD, 3(S + 12)(S - 12)

                                    

                                    0 = (S - 24)(S + 6)

                                    0 = S - 24     or      0 = S + 6

                                    Speed of boat, or     or     - 6 = S (ignore)