If a boat travels upstream and reaches Town A in 2 hours. the speed of the boat in still water is: D. 12 mph.
What is the speed?
Let denote the speed of the boat in still water as B and the speed of the stream as S.
The speed of the boat relative to the ground is:
Speed upstream = B - S
The speed of the boat relative to the ground is given by:
Speed downstream = B + S
The return trip takes 1 hour and 20 minutes which is equivalent to 1.33 hours.
Set up two equations:
Equation 1: Speed upstream × Time upstream = Distance
Equation 2: Speed downstream × Time downstream = Distance
Since the distance traveled in both directions is the same set the two equations equal to each other:
(B - S) × 2 = (B + S) × 1.33
Solve for B which is the speed of the boat in still water:
2B - 2S = 1.33B + 1.33S
2B - 1.33B = 2.66S
0.67B = 2.66S
B = 2.66S / 0.67
Substitute :
B = 2.66 × 3 / 0.67
B = 11.94 mph
B-= 12 mph
Therefore the speed of the boat in still water is approximately 12 mph.