Rational word problem about people swimming

Question

A person swims 11 miles downriver in the same time they can swim 7 miles upriver. The speed of the current is 4 miles per hour. Find the speed of the person in still water

Answer 1

(x + 4) t = 11

t = 11/(x+4)

 

(x - 4) t = 7

t = 7/(x - 4)

 

11/(x + 4) = 7/(x - 4)

11 (x - 4) = 7(x + 4)

11x - 44 = 7x + 28

11x - 7x = 28 + 44

 4x = 72

x = 18