Answer: Average speed of boat = 32mph
Step-by-step explanation: Full question: 5 hours 20mins. Find the average speed of the boat
Let average speed of boat be mph
Let time to travel downstream = 80/(x + 8 )
Let time to travel upstream = 80/( x - 8)
Total time = 51/3 hrs=16/3 hrs
80/(x +8) +80/(x-8) = 16/3
Multiply both sides with3(×+8)(x-8)
(X+8)(x-8) = (x+8)(x-8)/16
15(2x)=x^2-64
X^2 -30x - 64 =0
Factorizing,you get
(x - 32)(x + 2) => ×=32 or x= -2
x = 32mph
