Measurements of the observed cross sections for $e^+e^-\to$ exclusive light hadrons containing $\pi^0\pi^0$ at $\sqrt s= 3.773$, 3.650 and 3.6648 GeV

By analyzing the data sets of 17.3, 6.5 and 1.0 pb−1 taken, respectively, at s=3.773, 3.650 and 3.6648 GeV with the BES-II detector at the BEPC collider, we measure the observed cross sections for e+e−→π+π−π0π0, K+K−π0π0, 2(π+π−π0), K+K−π+π−π0π0 and 3(π+π−)π0π0 at the three energy points. Based on these cross sections we set the upper limits on the observed cross sections and the branching fractions for ψ(3770) decay into these final states at 90% C.L.