Answer:
57 mph
Step-by-step explanation:
Let b represent Bob's speed on the trip. Then his time is ...
time = distance/speed
Bob's time = 230/b
Then John's speed is b+8, and his time is ...
John's time = 230/(b+8)
The difference of their times is 1/2 hour:
Bob's time - John's time = 1/2
230/b -230/(b+8) = 1/2 . . . substitute the expressions for time
460(b+8 -b) = b(b+8) . . . . . multiply by 2b(b+8)
b^2 +8b -3680 = 0 . . . . . . .put in standard form
(b +4)^2 -3696 = 0 . . . . . . . add 16-16 to complete the square
b = -4 +√3696 ≈ 56.795 . . . solve for positive b
Bob's drove about 57 mph on the trip.
