SOLUTION: At 9pm, Lucy started to gallop her horse at 20 miles per hour to catch Edmund, who had a three hour head start, and if Lucy was still 40 miles behind at 11 pm, how fast was Edmund

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Question 142851: At 9pm, Lucy started to gallop her horse at 20 miles per hour to catch Edmund, who had a three hour head start, and if Lucy was still 40 miles behind at 11 pm, how fast was Edmund riding?
(PS: Please show how you got your answer, so I can see how you worked it. This problem is giving me major problems. It has been explained to me 2 different ways, but I don't understand either way. Thanks.)
Answer by psbhowmick(878) About Me  (Show Source):
You can put this solution on YOUR website!
Suppose, Edmund's speed is 'v' mph.
By that time Lucy rode for 2 hrs. (9 pm to 11 pm), Edmund rode for ( 2 + 3 =) 5 hrs. (since he started 3 hrs. early).

By 11 pm Lucy had rode a distance S%5BLu%5D+=+2+x+20+=+40 mph.
By 11 pm Edmund had rode a distance S%5BEd%5D+=+5+x+v+=+5v mph.

Since, still Lucy is 40 miles behind then,
Distance covered by Lucy + 40 miles = Distance covered by Edmund
40 + 40 = 5v
5v = 80
v = 80/5 = 16

Hence, Edmund rode at the speed 16 mph.