The price of a pen is increased by 45% and the quantity purchased is decreased by 25%. What is the percentage increase/decrease in the amount spent on the commodity?

8.75% 

                       Earlier        Later

           Price        20     :     29              [45% = \(\frac{9}{20}\) ]

         Quantity    4      :      3               [ 25% = \(\frac{1}{4}\) ] 

                       ---------------------

Expenditure         80    :    87          [Exp.= Price x Quantity]

Difference =       7 R

Effect on Exp. = \(\frac{7}{80}\) × 100 = 8.75% decrease