Question

A scale model of an airplane has a length of 19 centimeters and a wingspan of 18 centimeters. The length of the real airplane is 38 meters. What is the wingspan of the real airplane?

Answer 1

The wingspan is 36 m.

Using a proportion to solve this, we write the scale factor as a ratio first:  19/38, since 19 is the size of the model's length and 38 is the real length.  For the second ratio, we have 18 for the size of the model wingspan and x for the real wingspan:

19/38 = 18/x

Cross multiply:
19*x = 38*18
19x = 684

Divide both sides by 19:
19x/19 = 684/19
x = 36 m

Answer 2

For this case we can use the following rule of three:
 19 cm -------> 38 m
 18 cm -------> x
 From here, we clear the value of x.
 We have then:
 x = (18/19) * (38)
 x = 36 m
 Answer:
 The wingspan of the real airplane is:
 x = 36 m