Question

a contractor has a blueprint for a house drawn to the scale is 1in:3ft. A wall on the blueprint is 6.5 inches long. How long is the actual wall?

Answer 1

1/3 = 6.5/x (1 in to 3 ft = 6.5 in to x ft)
cross multiply
(1)(x) = (3)(6.5)
x = 19.5 ft

check...
1/3 = 6.5/19.5
cross multiply
(1)(19.5) = (3)(6.5)
19.5 = 19.5 (correct)

6.5 in = 19.5 ft (the measurement of the wall)