From a train station, one train heads north and another heads east. Some time later, the northbound train has traveled 16 miles. If the two trains separated by a straight-line distance of 20 miles, how far has the eastbound train traveled?

Answer: the eastbound train had travelled 12 miles

Explanation: using Pythagoras theorem, we know that

X^2 = a^2 + b^2

Where ^ stands for raised to power.

Let

a stand for the train going towards North and

b stands for the train going towards east.

X stands for the total distance between train a and b = 20 miles.

By Pythagoras rule

X^2 = a^2 + b^2

20^2 = 16^2 + b^2

400 = 256 + b^2 so that

b^2 = 400 - 256 = 144

b = √144

b = 12 miles.