Nội dung bài giảng
Bài 2. Tính:
a) 3 + \( \frac{2}{5}\) ; b) 4 - \( \frac{5}{7}\) ; c) 1 - \( \left ( \frac{2}{5} +\frac{1}{3}\right )\) .
Bài giải:
a) 3 + \( \frac{2}{5}\) = \( \frac{15}{5}+\frac{2}{5}=\frac{17}{5}\) ;
b) 4 - \( \frac{5}{7}\) = \( \frac{28}{7}-\frac{5}{7}=\frac{23}{7}\) ;
c) 1 - \( \left ( \frac{2}{5} +\frac{1}{3}\right )\) = 1 - \( \left ( \frac{6}{15} +\frac{5}{15}\right )\) = 1 - \( \frac{11}{15}\) = \( \frac{15}{15}-\frac{11}{15}=\frac{4}{15}\) .