A physical quantity Z depends on four observables a,b, c and d , as $\mathrm{Z}=\frac{{\mathrm{a}}^2{\mathrm{b}}^{\frac{2}{3}}}{\sqrt{\mathrm{c}}{\mathrm{d}}^3}$. The percentages of error in the measurement of a,b, c and d are 2%, 1.5%, 4% and 2.5% respectively. The percentage of error in Z is