1.105 Time from $t=0$ to $t=1$, the population increases by $i \%$, and from $t=1$ to $t=2$, the population increases by $j \%$; thus, from $t=0$ to $t=2$ the population increases by
(A) $(i+j) \%$.
(B) $i j \%$.
(C) $(i+i j) \%$.
(D) $\left(i+j+\frac{i j}{100}\right) \%$.
(E) $\left(i+j+\frac{i+j}{100}\right) \%$.
(42nd American High School Mathematics Examination, 1991)
[Solution] If $t=0$, the population is $m$, then when $t=1$, the population is $m(1+i \%)$; when $t=2$, the population is
$$
m(1+i \%) (1+j \%) = \left(1+i \%+j \%+\frac{ij}{100} \%\right) m,
$$

which means the population has increased by $\left(i+j+\frac{ij}{100}\right) \%$.
Therefore, the answer is $(D)$.