Answer:
1a. 8 miles per hour
1b. 32 km per hour
2a. 28 miles
2b. 3 hours
3a. 2925
3b. 1/4 hour or 15 minutes
Explanation:
For number 1a, think of 2 1/2 hours equals 20 miles as 2 1/2x=20. The x being hours, and the 20 being 20 miles. You want the equation to become x=?. So you divide 2 1/2x=20 by 2 1/2 to make the equation start with x=. You end up with x=8. Or you could just think of it as divide 20 miles by 2 1/2 hours. Either way, you end up with 8 miles per hour. For number 1b, you do the same thing as before, but you have to make 4 hours and 45 minutes a fraction. So, the are 60 minutes in an hour, so the fraction would be 45/60. Then you simplify that down to 3/4. So, 152 km divided by 4 3/4 is 32 km per hour.
For number 2a, set aside 30 minutes for now. She can go 24 miles in 3 hours. Because 8 miles times 3 hours equals 24 miles. It’s like instrad of 8 miles per hour, it’s 24 miles per 3 hours. Then, because 30 minutes is half of an hour, 8 divided by 2 would make it 4 miles per half an hour. So 24 plus 4 is 28 miles. For number 2b, you want to know how many hours it took to travel 1980 miles. Since you already knowmthat is takes one hour to go 660 miles, pretend that each 660 miles is one hour. So you divide 1980 by 660 so see how many one hours fit. You get 3. So, an airplane can fly 1980 miles in 3 hours.
For number 3a, like 2a, you basically multiply the constant speed by the full hours then the fraction, and add them together. You could also just multiply the constant speed by the number 3 3/4. That way you get the miles per 3 3/4 hours. 3 3/4 times 780 is 2925. So the plane can fly 2925. For number 3b, to get the 2 miles per ? hours, you have to divde 8 by 4 to get to 2. So you divide 1 hour by 4 to get the answer. So it’s 1/4, (one fourth of an hour) or 15 minutes 1/4 of 60 (the amount of minutes in an hour) for Mary to go 2 miles.