If the distance between two points on the ground is 10 miles and the distance between the same two points on a map is 4 inches, what is the map scale expressed as a ratio?

In order to get to the result, we need to see first how many inches on the map make up for one mile on the ground:

4/10 = 0.4

So we have 0.4 inches on the map for one mile on the ground.

Next we should take in consideration how much inches are there in one mile:

1 mile = 63,360 inches

Since in this case we have 0.4 inches for one mile on the ground, the amount of inches in a mile should be divided by 0.4 in order to get to the ratio:

63.360 / 0.4 = 25,344

So the ration on the map is 158,400.