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Answer:
1.8 miles
Explanation:
In the first half hour, Sandra hikes 9/10 = 0.9 miles. She hikes that distance again in the second half-hour. After an hour, Sandra has hiked ...
2 × 0.9 miles = 1.8 miles
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If you like, you can consider it a "unit rate" problem. To find miles per hour, divide miles by hours:
(9/10 mi)/(1/2 h) = (9/10)(2/1) mi/h = 9/5 mi/h = 1.8 mi/h
Sandra hikes 9/5 or 1.8 miles in an hour.