9514 1404 393
Answer:
20 miles
Explanation:
The north and east distances form the legs of a right triangle. The straight-line distance between the trains is the hypotenuse of that triangle. The Pythagorean theorem can be used to find the length of the hypotenuse (d).
d² = 12² +16²
d² = 144 +256 = 400
d = √400 = 20
The two trains are 20 miles apart.
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Additional comment
You may recognize the given distances are in the ratio 3 : 4. You may recall that side ratios of 3 : 4 : 5 make a right triangle. If so, you recognize that the straight-line distance is (4 miles)×5 = 20 miles. (3:4:5 right triangles show up often in algebra and geometry problems, so might be something you want to look for.)