posted by Kelvin on .
a boat moves through still wather at x kilometers(km) per hour. it travels 24km up stream against a current of 2km per hour and then returns with the current. The rate upstream is x-2 because the boat moves against the current and the rate downstream is x+2 because the boat moves with the current.
36.write an expression for the total time for the round trip.
37.write your answer to exercise 36 as a single rotional expression.
28.use your answer to exercise 37 to find how long the round trip will take if the boat travels 10kilometers per hour through still water
time upstream = 24/(x-2)
time downstream = 24/(x+2)
total time = 24/(x-2) + 24/(x+2)
common denominator is (x+2)(x-2)
so total = (24(x+2) + 24(x-2))/((x+2)(x-2))
= 48x/(x^2 - 4)
Plug in x=10