Question 264293
Hello, 
The key to understanding these types of problem is getting what "per" means in "miles per hour". 
"per" means "in each". So if a person travels 30 miles "in each" hour then how many miles does he drive in 10 minutes. Since there are six 10 minutes in an hour then we can divide 6 into 30 to get 5 miles in ten minutes. Of course for 20 minutes we'd have 10 miles. 
Granted this might be tough for a 3rd grader to get so I suggest you draw a line that goes from a start to finish measuring 30 miles in 1 hour then break down the units into 6 equal parts.  
Or take a ride in the car and go 30m/h for 20 minutes and see what the odometer says. 
RJ
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