(18 nCr 7 * 11^11) + (18 nCr 8*11^10) + (18 nCr 9*11^9) +(18 nCr 10*11^8) +(18 nCr 11*11^7) + (18 nCr 12*11^6) + (18 nCr 13 * 11^5) + (18 nCr 14 * 11^4) + (18 nCr 15 * 11^3) + (18 nCr 16 * 11^2) + (18 nCr 17 * 11^1) + (18 nCr 18 * 11^0)==
(907975 8605524464, 113496 9825690558, 11464 3416736420, 937 9915914798, 62 0159729904, 3 2887258404, 1379884968, 44801460, 1086096, 18513, 198, 1, 0, 0, 0, 0, 0, 0, 0)==1033940 6236645784 /12^18== 0.000388358 - probability of at least 7 out of 18 people.
(18 nCr 7) * (11^11)==9079758605524464 / 12^18== 0.000341045 - probability of exactly 7 out of 18 people.