Mathematics for IGCSE & O level - Proportion (Section 1 - No. 6)
If the area of a square is directly proportional to the square of the side length, and a square with side length 3 has an area of 9, what is the area of a square with side length 5?
15
20
25
30
Εξήγηση
Area = k * side^2, 9=k*3^2, then k=1. Therefore area = side^2. So, when the side is 5, area is 25