Question 593284
Dante rides his bike 8 miles per hour, racing the fastest spider.  After a half-hour, the spider is 1 mile ahead of him.
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In 1/2 hr, Dante went 4 miles (8 mi/hr * 0.5 hr)
The spider is 1 mile ahead --> 5 miles in 0.5 hr
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d = r*t
r = d/t = 5/0.5
r = 10 mi/hr
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In absolute terms, the fastest spider is the camel spider that lives in hot, desert regions. This eight-legged speedster can run across sand at an impressive 10-12 mph.
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I think that's the answer you wanted, since you said it was 10.  But, you asked "how long can it crawl?" 
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PS  All spiders have eight legs.