17.现有6张不同的卡片,其中红色、黄色卡片各3张,从中任取2张,则这2张卡片不同颜色的概率为( )
| A. | $\frac{3}{10}$ | B. | $\frac{1}{5}$ | C. | $\frac{2}{5}$ | D. | $\frac{3}{5}$ |
16.已知数列{an}满足a1=a,a2=b,an+2=an+1-an(n∈N*),Sn是{an}的前n项的和,则a2016+S2016=( )
| A. | a+b | B. | a-b | C. | -a+b | D. | -a-b |
15.设等差数列{an},{bn}的前n项和分别为Sn,Tn,若对任意自然数n都有$\frac{S_n}{T_n}$=$\frac{2n-3}{4n-3}$,则$\frac{a_6}{b_6}$的值为( )
| A. | $\frac{19}{41}$ | B. | $\frac{3}{7}$ | C. | $\frac{7}{15}$ | D. | $\frac{1}{3}$ |
12.设等差数列{an}的前n项和为Sn,若a1+a3+a5=3,则S5的值为( )
0 229683 229691 229697 229701 229707 229709 229713 229719 229721 229727 229733 229737 229739 229743 229749 229751 229757 229761 229763 229767 229769 229773 229775 229777 229778 229779 229781 229782 229783 229785 229787 229791 229793 229797 229799 229803 229809 229811 229817 229821 229823 229827 229833 229839 229841 229847 229851 229853 229859 229863 229869 229877 266669
| A. | 5 | B. | 7 | C. | 9 | D. | 11 |