Question

Craig ran the first part of a race with an average speed of 8 miles per hour and biked the second part of a race with an average speed of 20 miles per hour. The entire two-part, 15-mile race took him 1.125 hours to complete. Which table correctly represents his rates, times, and distances for each part of the race?

Answer 1

Then, 15 - x is the distance ran in the second part.
The time, t1, for the first part is t1 = xmi / 8mi/h
The time, t2, for the second part is t2 = (15 - x)mi / 20mi/h
The total time is t1 + t2 = 1.125 h
Then x/8 + (15 - x) / 20 = 1.125
To solve for x, multiply both sides by 40 (this is the least common multiple)
5x + 30 - 2x = 45
3x = 15

to find x divide: 15/3=5

And 15 - x = 10 mi.
First part:
Speed: 8mi/h
Distance: 5 mi
Time: 5mi/8mi/h = 5/8 h = 37.5 minutes
Second part
Speed: 20 mi/h
Distance: 10 mi
Average speed: 15mi/1.125h =13.33 mi/h
Distance: 15mi
Time: 1.125 h = 67.5 minutes 

Answer 2

the correct answer is A