$1 \cdot 125 x y^{2}$ In this expression, the values of $x$ and $y$ each decrease by $25 \%$; then the value of this expression is
(A) Decrease by $50 \%$.
(B) Decrease by $75 \%$.
(C) Decrease by $\frac{37}{64}$ of its value.
(D) Decrease by $\frac{27}{64}$ of its value.
(E) None of the above.
(4th American High School Mathematics Examination, 1953)
［Solution］From the problem, we notice that
$$
(1-25 \%) x \cdot[(1-25 \%) y]^{2}=(1-25 \%)^{3} x y^{2}=\left(\frac{3}{4}\right)^{3} x y^{2} \text {, }
$$

and
$$
1-\left(\frac{3}{4}\right)^{3}=\frac{37}{64} \text {. }
$$

Therefore, the answer is $(C)$.