Question

To make a model of the Guadalupe Tiver bed, hermonie used 1inch of clay for 5 miles of the rivers actual length. His model river was 50 inches long how long is the Guadalupe river ?

Answer 1

We have a model at scale of the river.

The scale is 1 inch in the model = 5 miles in the actual river.

We know that his model was 50 inches long, so we can calculate the actual length as:

$L=50in\cdot\frac{5mi}{1in}=250mi$

NOTE: we multiply the length of the model by the scale, in a way that the units of the model cancel each other (inches divided by inches, in this case). If we we want to find the actual length, the scale of the model goes in the denominator and the scale of the actual length goes in the numerator.

Answer: the actual length of the river is 250 miles.