回复：用天平称乒乓球

Step 1: Put 4 balls on each side if they are of the same weight, this should be easy, it is easy.
Step2. If they are not the same.
Name the heavy 4 as ABCD, the light 4 as EFGH, and the other 4 as IJKL

Check ABE and CFG
If ABE=CFI it is DGH step3: if G>H it is H(l)
If G If G=H it is D(h)
If ABE>CFI it is ABF step 3: A>B it is A(h)
A A=B it is F(l)
If ABE