Question 24531
the beauty of maths or the power of maths is that you learn the basic approach, the basic methods and then you can learn to apply those to harder situations.


Let speed of boat = x mph
Let speed of current = y mph


So, with the current:
her speed will be x+y. Takes 2 hours to go 9 miles.


Speed = distance/time so
x+y = 9/2
--> x+y = 4.5


and against the current:
her speed will be x-y. Takes her 6 hours to go the same 9 miles.


Speed = distance/time so
x-y = 9/6
--> x-y = 1.5


So, we have 2 unknowns and 2 equations. This is solveable.


x+y = 4.5
x-y = 1.5


Add them together... 2x = 6 --> x = 3mph


So, x+y = 4.5
then 3+y = 4.5
--> y = 1.5 mph


So, her speed is 3mph and river is 1.5 mph


Check in second equation, to makes sure:
x-y = 1.5
3-1.5 is indeed equal to 1.5, so correct


jon.