Let, the length of the rectangle be x cm and the breadth of the rectangle  y cm

Therefore area of the rectangle = x * y = xy cm²

as the length is increased by 50%

∴ length = x + 50% of x

            = x + 50/100 *x

            = x + x/2

            = 3x/2

Given that area is constant

so, xy = 3x/2 * breadth

breadth = 2xy/3x = 2y/3 cm

Percentage of increase in breadth = decrease in breadth/original breadth *100

                                                            = (y - 2y/3)/y * 100

                                                            =   ((3y - 2y) / 3)/y*100

                                                            = y/3y *100

                                                            = 100/3

                                                            = 33.333%

The breadth is decreased by 33.333% (Ans)