(1 cm)^2 ⇒ (10 mi)^2 = 100 mi^2 . . . on the first drawing
(1 cm)^2 ⇒ (30 mi)^2 = 900 mi^2 . . . on the second drawing
The area on the second drawing is 900/100 = 9 times as great.
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These are the areas represented by 1 square cm on the scale drawing. If the drawing is larger, then the represented area is correspondingly larger. The ratio of represented areas is still 9 times for drawings of the same size.
