However, a model was used for the beetle that was really only 20 inches long.
In the given problem, we have to find the time taken by a person to type 390 words if the person takes 1 minute to type 30 words. This fraction must be proportional to the second fraction.
The second fraction has '390 words' in the numerator and the variable 'x' to represent the time which we have to find.
Sam tried using a ladder, tape measure, ropes and various other things, but still couldn't work out how tall the tree was. That is OK, you simply have twice as many stones as the number in the ratio ...
so you need twice as much of everything to keep the ratio.