15. Evaluate
$$
\frac{678+690+702+714+\cdots+1998+2010}{3+9+15+21+\cdots+327+333} .
$$
15. Ans: 16 .
Note that both numerator and denominator are arithmetic progressions. Removing common factors gives
$$
\begin{aligned}
& 2 \times \frac{113+115+117+\ldots+333+335}{1+3+5+\ldots+109+111} \\
= & \frac{2 \times \frac{112}{2}(335+113)}{\frac{56}{2}(111+1)}=16 .
\end{aligned}
$$