1, derived from arithmetic progression's general formula: a5 = a1+(5-1) da1= 0, and then derived from the summation formula:

s 10 = na 1+n(n- 1)d/2 = 10 * 0+ 10 * 9 * 2/2 = 90

2. A4+A6 = A3+A7 = A2+A8 = A1+A9 =15, and the sum formula S9 = N (A1+A9)/2 = 9 *15/2 = 67.

3. According to the general formula of geometric series: B4 = b1* q (n-1) = 2 * 3 = 54, b5=b4*q=54*3= 162.

Then, the summation formula gives S5 = (b1-b5 * q)/(1-q) = (2-162 * 3)/(1-3) = 242.