SOLUTION: Mary left home at 12 noon and drove to visit her mom who lives 20 miles away. After she arrived she stayed for 2 hours. Afterwards, she drove to her friend Sue's house who lives 1

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Question 82909: Mary left home at 12 noon and drove to visit her mom who lives 20 miles away. After she arrived she stayed for 2 hours. Afterwards, she drove to her friend Sue's house who lives 15 miles from her mom. She arrived at Sue's at 3:00pm. If her speed heading for Sue's was 5 mph faster than her speed going to her mom's, find her average speed on the way to Sue's
Answer by josmiceli(19441) (Show Source):
You can put this solution on YOUR website!
The time spent driving plus the 2 hours at her mom's adds up to the
elapsed time of 3 hours (noon to 3 PM).
If s is the average speed to her mom's, then s+5 is the average speed
from her mom's to Sue's

This is just

Multiply both sides by

Use the formula

(note that the other answer is negative and
therefore makes no sense)

But the average speed going to Sue's is

mph answer
check answer

Is this true when ?

OK