The operation $\diamond$ is defined by $a \diamond b=a^{2} b-a b^{2}$. The value of $2 \diamond 7$ is
(A) -140
(B) -70
(C) 0
(D) 70
(E) 140
By definition, $2 \diamond 7=2^{2}(7)-2\left(7^{2}\right)=4(7)-2(49)=28-98=-70$.

ANswer: (B)