Raymond B. answered 05/29/19
Math, microeconomics or criminal justice
Speed = distance divided by time driving. The mountainous travel is 70 miles, making the level travel 250 miles. 70/(7-x) = 250/x - 14. Mountainous speed = level speed - 14 mph. Simplify the equation to 14x2 - 418x + 1750 = 0. Solve for x using the quadratic formula. 250/x = level speed. 70/(7-x) = mountainous speed. Alternatively, pick an easy number to use, let x=5, then 7-x=2. That's 2 hours in the mountains, 5 hours level travel. So speeds are 70/2=35 mph and 250/5= 50 mph. 50-35=15 mph which is fairly close to the required 14 mph difference. IF you do the tedious calculations correctly, the speeds should come out close to 35 and 50 mph. IF this were a multiple choice test, the correct answer would be the one very close to 35 and 50, and you would not have to take major time doing the calculations. That can be useful for time pressure tests.