



 
Hi Michael, Tina's average speed is her total distance divided by the total time. It doesn't seem there is enough information here because you can't find the distance she swims or the time it takes, but let's try anyway. Let the distance she travels upstream be d miles and the time it takes her to swim this distance be t hours. Since upstream she swims at 1 mph
and hence
(That looks strange since the units of d are miles and the units of t are hours, but it just means that the numbers d and t are the same.) Downstream she travels the same distance but at 4 mph. How long does it take her?
Penny Michael wrote back
Michael, My intention was not to do the question for you but to break it down into steps so that you could complete it yourself. I started by letting d be the distance she travells upstream and t be the time it takes for this part of the trip. I then observed that since she travells 1 mph going upstream the numbers d and t are the same. Furthermore I know that going downstream the distance she travells is also d miles. Then I asked
Downstream she travells at 4 time the speed as going upstream so It will take her 1/4 the time. Hence the time to travel Now can you answer the remaining three questions?
Penny  


Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences. 