树上小鸟飞走了20只，还剩9只，树上原来有多少只小鸟？6A*`,Y:K(q3H/u(x.j'`7k
算式：提示6O5~9K+n1L+e8]6A*`,Y:K(q3H/u(x.j'`7k
答：树上原来有0K8~9K0a9N+v,L)m7^9K)S只小鸟。6A*`,Y:K(q3H/u(x.j'`7k