$28 \cdot 29$ Last year, a bicycle cost 160 yuan, and a helmet for cycling cost 40 yuan. This year, the price of the bicycle increased by $5 \%$, and the price of the helmet increased by $10 \%$. The combined price increase for the bicycle and helmet is
(A) $6 \%$.
(B) $7 \%$.
(C) $7.5 \%$.
(D) $8 \%$.
(E) $15 \%$.
(44th American High School Mathematics Examination, 1993)
[Solution] Last year, the bicycle and helmet together were worth $160+40=200$ dollars. This year, the bicycle increased by $0.05 \cdot 160=8$ dollars, and the helmet increased by $0.10 \cdot 40=4$ dollars.
So this year, the bicycle and helmet together increased by 12 dollars, with a growth rate of $\frac{12}{200}=6 \%$. Therefore, the answer is $(A)$.