Bài 2 :
a, \(3+\dfrac{2}{5}\)
= \(\dfrac{15}{5}+\dfrac{2}{5}\)
= \(\dfrac{17}{5}\)
b, \(4-\dfrac{5}{7}\)
= \(\dfrac{28}{7}-\dfrac{5}{7}\)
= \(\dfrac{23}{7}\)
c, \(1-\left[\dfrac{2}{5}+\dfrac{1}{3}\right]\)
= \(1-\left[\dfrac{6}{15}+\dfrac{5}{15}\right]\)
= \(\dfrac{15}{15}-\dfrac{11}{15}\)
= \(\dfrac{4}{15}\)
Bài 2
a, 3 + \(\dfrac{2}{5}\) = \(\dfrac{15}{5}\) + \(\dfrac{2}{5}\) = \(\dfrac{17}{5}\)
b, 4 - \(\dfrac{5}{7}\) = \(\dfrac{28}{7}\) - \(\dfrac{5}{7}\) = \(\dfrac{23}{7}\)
c, 1 - ( \(\dfrac{2}{5}\) + \(\dfrac{1}{3}\))
= 1 - (\(\dfrac{6}{15}\) + \(\dfrac{5}{15}\))
= 1 - \(\dfrac{11}{15}\)
= \(\dfrac{15}{15}\) - \(\dfrac{11}{15}\)
= \(\dfrac{4}{15}\)