math
posted by alicia .
i cannot seem to make this work. If two trains leave the station at the same time, one traveling north and the other traveling south. the express travels 14 mph faster than the local. after 3 hours they are 315 miles apart. what is the rate of each train.
this is what I figured:
r * t= d
y=x+14.
3x + 3y= 315

I used to make my students draw up a chart for these type of questions, having 3 columns for (D)istance, (R)ate, and (T)ime, and two rows for the different situations, in this case North and South
..........D....R.....T
north .. 3x .. x ... 3
south 3(x+14) x+14 .. 3
Now use the information that the sum
of the two distances is 315 to get
so 3x + 3(x+14) = 315
easy from there.
Why are you using 2 unknowns ?
Notice that if you subbed in your first equation into your second, you would get my equation.