BOATS AND STREAMS

      b  --->  Boat speed/Man speed in water.

      c  --->  Current Speed/Speed of the River.

      d  --->  Down stream speed.

      u  --->  Up stream speed.

      D  --->  Total distance travelled.

      T  --->  Total time.

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1.

d=b+c

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2.

u=b-c

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3.

b=(d+u)/2

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4.

c=(d-u)/2

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5.Average Speed=(2xy)/x+y      i.e

(b2-c2)/b

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6.

D=[T(xy)]/x+y=[T(b2-c2)]/2b

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7.

T=(D*2b)/b2-c2

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8.

T=(D/d)+(D/u)=[D/(b+c)]+[D/(b-c)]