text: Hey guys, the question asks for a SERIES, not a SEQUENCE.\n\nthe formula for any geometric series for n terms is given by:\n\na * [1-r^(n+1)] / (1-r)\n\nwhere a is the first term, r is the ratio, and n is the # of terms\n\nFor example, in your case, for 6 terms,\n\nyou'll have S(6) = 27 * (1-(-1/3)^6)/(1-(-1/3))\n\nfor 5 terms: \n\nS(5) = 27 * (1-(-1/3)^5)/(1-(-1/3))\n\nand so on ...