5.5×6.6+6.6×7.7+7.7×8.8+8.8×9.9．

5.5×6.6+6.6×7.7+7.7×8.8+8.8×9.9
=1.1×5×1.1×6+1.1×6×1.1×7+1.1×7×1.1×8+1.1×8×1.1×9
=1.1×1.1×5×6+1.1×1.1×6×7+1.1×1.1×7×8+1.1×1.1×8×9
=1.21×30+1.21×42+1.21×56+1.21×72
=1.21×（30+42+56+72）
=1.21×200
=242．