3. In two hours, Allice drove her car the same distance that Gene drove his car in 2 hours and 30 minutes. Find the speed of Gene's car given that he drove 10 mph slower than Alice drove.
4. A cruiser and a submarine leave the same port at the same time and travel eastward. The cruiser average 18 mph and the submarien 42 mph. For what period of time will the cruiser be 12 miles or less behind the submarine?
6. The numerator of a fraction is 5 less than the denominator. If the numerator were increased by 3 and the denominator increased by 4, the resulting fraction would be 1/2. Find the original fraction.
3. Suppose the speed of Gene's car is x mph. Since he drove 10 mph slower than Alice drove, then the speed of Alice's car is x+10 mph. So Alice drove 2(x+10) miles in two hours and Gene drove 2.5x miles in 2 hours and 30 minutes. From the condition, we get the equation
2(x+10)=2.5x, then 2x+20=2.5x, then 0.5x=20, then ...
Speed and distance word problems are solved. The period of time a submarine will cruise at 12 miles is determined.