SOLUTION: It took Gina 3.6 hours to drive to her mother's house on thursday morning.On her return trip on friday night, traffic was heavier,so it took her 4 hours.Her average speed on friday

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Question 838510: It took Gina 3.6 hours to drive to her mother's house on thursday morning.On her return trip on friday night, traffic was heavier,so it took her 4 hours.Her average speed on friday was 4 mph slower than on thursday. What was her average speed on friday ?
Answer by josgarithmetic(39613) About Me  (Show Source):
You can put this solution on YOUR website!
The distance is the same both ways, both days.

_____________speed_________time__________distance
Thursday_____r_____________3.6___________d
Friday_______r-4___________4_____________d

That's one way to arrange the data. The question is, "speed on friday". We can reassign the rate variable like this:
_____________speed_________time__________distance
Thursday_____r+4___________3.6___________d
Friday________r____________4_____________d
The rate on Friday is still 4 mph slower than thursday, so this data arrangement should still work.


RT=D, typical meanings, so we should understand adding this information:
_____________speed_________time__________distance
Thursday_____r+4___________3.6___________d=(r+4)(3.6)
Friday________r____________4_____________d=r*4

All needed is to solve for r in %28r%2B4%29%283.6%29=r%2A4, rewritten as highlight%28%283.6%29%28r%2B4%29=4r%29