Answers

1. Answer:

   5 km/h

   Step-by-step explanation:

   Speed of man in still water = s

   Speed of current = c

   Speed upstream = s – c

   Distance upstream = 24 km

   Time upstream = 6 hours

   Speed downstream = s + c

   Distance downstream = 36 km

   Time downstream = 6 hours

   Speed Equation

   speed = distance/time

   distance = speed × time

   d = st

   We write a distance equation for upstream and a second distance equation for downstream.

   Upstream:

   d = st

   24 = (s – c) × 6

   Divide both sides by 6 and switch sides:

   s – c = 4        Equation 1

   Downstream:

   d = st

   36 = (s + c) × 6

   Divide both sides by 6 and switch sides.

   s + c = 6       Equation 2

   We now have two equations in two variables. We use equations 1 and 2 as a system of equations.

   s – c = 4

   s + c = 6

   Add the equations to use the addition method.

   2s = 10

   s = 5

   Answer: 5 km/h

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