This will make 7.5 x 1.009 higher than just 7.5 because 1.099 is higher than 1. And anything times 1 equals itself, so that means that if you times it by something higher than that, then the main number will go higher. If we do 0.951, then that won't work out because that will decrease the value of 7.5 since it is lower than 1. And if we do just 1, that will keep 7.5 to itself. So, the only option left is 1.099, and this option IS the right one.
Let the boat speed in still water be b. Let the current speed be c. The speed going upstream is 20/4 = 5 mph. The speed going downstream is 32/4 = 8 mph. b - c = 5 ........(1) b + c = 8 .......(2) Adding equations (1) and (2) we get: 2b = 13 b = 13/2 = 6.5 Plugging in the value for b into equation (1) we find c = 1.5. The boat speed in still water is 6.5 mph and the current speed is 1.5 mph.
