Вычислите: 4,05 − \(−\frac{1}{2}\)^2\(1\frac{2}{3} : 2,5 − 3\).

\[4.05-\left(-\frac{1}{2}\right)^2\left(1\frac{2}{3}:2.5-3\right)\]

\[1\frac{2}{3}=\frac{5}{3},\qquad \left(-\frac{1}{2}\right)^2=\frac{1}{4}.\]

\[\frac{5}{3}:2.5=\frac{5}{3}:\frac{5}{2}=\frac{2}{3},\qquad \frac{2}{3}-3=-\frac{7}{3}.\]

\[4.05-\frac{1}{4}\cdot\left(-\frac{7}{3}\right)=4.05+\frac{7}{12}=\frac{81}{20}+\frac{7}{12}=\frac{271}{60}=4\frac{31}{60}.\]

Ответ: \(4\frac{31}{60}\).