algebra word problem?
A boat traveled downstream a distance of 90mi and then came right back. If the speed of the current was 20mph and the total trip took 6 hours, find the average speed of the boat relative to the water.
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Assume the speed of the boat = x mph.
Then the time taken for the round trip =
90/(x+20) + 90/(x-20) = 6 hrs given
simplifying this gives the quadratic :
x² - 30 x - 400 = 0
which gives average speed: x = 40 mph