Solution:
Given:
The sides of two similar triangles are in the ratio 9 : 4.
Concept used:
When two triangles are similar, the ratio of their areas is equal to the square of the ratio of their corresponding sides.
Calculation:
Let the ratio of the areas of these triangles be A1 : A2.
⇒ A1 : A2 = 92 : 42
⇒ A1 : A2 = 81 : 16
∴ The ratio of the areas of these similar triangles is 81 : 16.