Find the MPH of the boat when it goes upstream... 3h / 6m = 1h / 2m So, 2mph Speed of the boat - current = 2mph - > x - y = 2 Find the MPH of the boat going downstream... 3h / 18m = 1h / 6m So, 6mph x + y = 6 We now have a system of equation, let's solve it!
x - y = 2 -> x = y + 2 x + y = 6 - > (y + 2) + y = 6 -> 2y + 2 = 6 -> 2y = 4 -> y = 2 This is the speed of the current! Subtitute y = 2 in the first equation: x - 2 = 2 x = 4 This is the speed of the boat Rate of the current = 2mph Rate of the boat in still water = 4mph
Aliaa got a mark of 60 in her first 4 tests, so her total mark is 60 x 4 = 240. On her fifth test, she got a mark of 80. So her average is: (240+80)/5 = 320/5 = 64 Her avg is 64 (c).
