Question

已知m和2n的等差中项是4,2m和n的等差中项是5,则m和n的等差中项是(    )

A.2                B.3                   C.6                  D.9

Answer 1

B

解析:m+2n=8,2m+n=10,两式相加得3m+3n=18,即m+n=6=2×3.