Tính: (89,45 + left( { – 3,28} right) + 0,55 + left( { – 6,72} right))

(begin{array}{l}89,45 + left( { – 3,28} right) + 0,55 + left( { – 6,72} right)\ = 89,45 + 0,55 + left( { – 3,28} right) + left( { – 6,72} right)\ = left( {89,45 + 0,55} right) + left[ {left( { – 3,28} right) + left( { – 6,72} right)} right]\ = 90 + left( { – 10} right)\ = 90 – 10\ = 80end{array})