Answer:
Rate of the boat in still water 73 mi/hr
Rate of the current 18 mi/hr
Explanation:
Calculation to determine the rate of the boat in still water and the rate of the current
Let B represent the speed of the boat in still water.
Let S represent the speed of the stream
Speed upstream = B-S.
Speed downstream = B+S.
Using the equation for distance
Distance=Rate * Time
Upstream
(B-S)7 = 385
(B+S)5= 455
Simplify first:
B-S=385/7
B-S = 55
B+S=455/5
B+S = 91
Solve by elimination. Add the two equations.
2B=55+91
2B = 146
B=146/2
B = 73 mi/hr
Substitute this into either equation and solve for S.
B+S = 91
73+S = 91
S=91-73
S = 18 mi/hr
Therefore the rate of the boat in still water is 73 mi/hr and the rate of the current is 18 mi/hr