Jawabanmu

2014-02-05T21:20:24+07:00
5+7+9+11+13+15+17+19+21+23+25+27 = 192
2014-02-05T22:15:54+07:00
A = 5 
b = 2

Sn = n/2 (2a+(n-1)b)
192 = n/2 (2x5 + (n-1) 2)
192 = n/2 (10+2n-2)
384 = n (10+2n-2)
384 = 2n^2+10n-2n
384 = 2n^2+8n
maka n = 12