Michael C. answered • 03/02/17

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Let the swimmer's speed in still water be x, and the speed of the current be y

speed against current = x - y = 200/8 = 25 meters per minute (speed = distance/time)

speed with current is x + y = 200/4 = 50 meters per minute

therefore solving a system of linear equations:

x - y = 25 (1)

x + y = 50 (2)

(1) + (2) gives 2x = 75; or x = 75/2 =

**37.5**meters per minute (swimmers speed)from (2) y = 50 - x = 50 - 37.5 =

**12.5**meters per minute (speed of current)Method 2

x - y = 25 (1)

x + y = 50 (2)

x + y = 50 (2)

from (1) x = 25 + y (3)

substituting (3) into (2) 25 + y + y = 50

25 + 2y = 50; 2y = 50 - 25 = 25; therefore y = 25/2 =

**12.5**from (1) x - 12.5 = 25, this gives x = 25 + 12.5 =

**37.5**