Answer:
15 mi/h
Step-by-step explanation:
In 1/2 hour at 10 mi/h, Omar covered 5 miles, the distance to the store. At 3 times the speed (30 mi/h), he covered the same distance in 1/3 the time on the way home: 1/6 hour.
His total distance was 2·(5 mi) = 10 mi.
His total time was (1/2 h) +(1/6 h) = 2/3 h.
His average speed was (10 mi)/(2/3 h) = 15 mi/h.
