Julie drives 100 mi to Grandmother's house. On the way to Grandmother's, Julie drives half the distance at 39.0 mph and half the distance at 61.0 mph . On her return trip, she drives half the time at 39.0 mph and half the time at 61.0 mph . What is Julie's average speed on the way to Grandmother's house? What is her average speed on the return trip?
1)
on the way to Grandmother’s house:
total time taken = half distance / speed for this + half distance / speed for this
= 50 mi / 39.0 mph + 50 mi / 61.0 mph
= 2.10 h
average speed = total distance / total time
= 100 mi / 2.10 h
= 47.6 mph
Answer: 47.6 mph
2)
on the return trip:
total time taken = half distance / speed for this + half distance / speed for this
= 50 mi / 39.0 mph + 50 mi / 61.0 mph
= 2.10 h
average speed = total distance / total time
= 100 mi / 2.10 h
= 47.6 mph
Answer: 47.6 mph
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