Monday, March 10, 2008

Time and Distance Problem 5 Solution

This is similar to the previous problem. The only difference is that they left at a certain time and you have to figure out what time they end up being 2100 miles apart.

Once again, they're both covering distance individually that adds to the total distance were looking for 2100, therefore we can just add their respective speeds to figure out how long it will take to cover that distance.

So with x being used as "time", 300 and 600 the respective speeds or rates to be added, and 2100 the distance --- rate X time = distance we have....

600x + 300x = 2100

900x = 2100

x = 2100/900

x = 2 and 1/3 hours or 7/3 of an hour

So to get the time in hours from when they left we can either figure out a what a third (1/3) of an hour is an add it to 2 (2 and 1/3 hours) or we can figure out how many minutes (7/3) X 60 would be..

1/3 of an hour is (1/3) X 60 or 60/3 which is 20-- so 20 minutes added to 2 is 2 hours and 20 minutes which is the answer but the alternate approach would be taking
(7/3) X 60 and you end up with 420/3 which is 140 or 140 minutes --- with 60 minutes in an hour you can see that 2 hours is 120 minutes with 20 minutes left over and once again 2 hours and 20 minutes

This is still not the answer the problem is looking for. It's asking what time were they that far apart. If they left at 12 (noon) , 2 hours and 20 minutes later would be 2:20 pm--- So 2:20 pm is the answer.

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