x y 4 11 14 11 23 11 32 42 xx += ++ ++ ++ 1 11 12 11 34 56 yy += ++ ++ .; 29 24 1459 12556 =-= yx x 11 1ab x ab x+-=+ a b a b x a b 2 2 441 4 ba b -+ x ch sau: M = 2222255555 x 2222266666, N = 20032003 x 20042004 Ñaùp soá: M=4 51,587% S S ABCD DEC » Δ 43,86% S S BDC ABD » (5 7) (5 7) 27 nn + 35 35 2 22 nn æöæö +- +- ç÷ç÷ ç÷ç÷ èøèø