Suatu seri: 11-19-10-20-9-21-8 seri selanjutnya :

22

Polanya adalah (A) - (B) - (A-1) - (B+1) - (A-2) - (B+2) - (A-3) - (B+3) dan seterusnya

Semoga membantu

pola = - + - +

11 + [-8]= -19
-19 + [9] = -10
-10 + [-10] = -20
-20 + [11] = -9
-9 + [-12] = -21
-21 + [13] = -8

maka selanjutnya 
-8 + [-14] = -22