The side of a square is increased by 25%. What is the percentage increase in its area?

56.25%

25% = $\frac{1}{4}$

Side                 Old   :   New

                        4     :     5

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Area                 16    :    25

Area of square = Side²

Percentage change in area = $\frac{25 - 16 }{16}$ × 100

=  $\frac{25 - 16 }{16}$ × 100

= 56.25%