Is my use of AC method incorrect?

bobisaka said:
6r = 10

6r/6 = 10/6

r = 1.666 = 1.67

Uphill 1.67 - 5 = -3.33mph
Downhill = 1.67mph

t = 20/-3.33 = -6.01
t = 20/1.67 =11.98
Total hours = 5.97 = 6 = 6 hours

so it is correct; they are both correct . Now, am i on the right track?

I will keep that in mind, I will do a thorough check of all answers before passing them.
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How did 6r = -10 become 6r = 10?? Does 10 = -10? Students must realize that -10 and 7 are as different as -10 and 10. They may look the same but they are different.
 
bobisaka,
You asked if it ok to reject r=-10/6. I suggested that you should decide. I even asked you what it meant for the rate to be negative. Did you think about what that meant? After discovering that r = -10/6 you went and found out that the speed uphill would be negative.

You need to slow down a bit and think logically. You ruled out r= -10/6 and let it become r= 10/6 since you felt that the rate should be positive. So why would you then let another rate be negative?

You need to think if rates can be negative and what would that mean. Seriously, before you move on with this problem you have to think about that. Please let us know what you conclude. Also, don't make your final decision based on this problem. By the way yesterday I drove by car in reverse.
 
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