\(a,\dfrac{7}{15}+\dfrac{4}{5}=\dfrac{7+4\times3}{15}=\dfrac{19}{15}\\ b,\dfrac{2}{3}-\dfrac{3}{8}=\dfrac{2\times8-3\times3}{24}=\dfrac{7}{24}\\ c,\dfrac{4}{5}\times\dfrac{5}{8}=\dfrac{1\times1}{2\times1}=\dfrac{1}{2}\\ d,\dfrac{1}{2}:\dfrac{2}{5}=\dfrac{1}{2}\times\dfrac{5}{2}=\dfrac{5}{4}\)
a) \(\dfrac{7}{15}+\dfrac{4}{5}\)
\(=\dfrac{7}{15}+\dfrac{12}{15}\)
\(=\dfrac{19}{15}\)
b) \(\dfrac{2}{3}-\dfrac{3}{8}\)
\(=\dfrac{16}{24}-\dfrac{9}{24}\)
\(=\dfrac{7}{24}\)
c) \(\dfrac{4}{5}\times\dfrac{5}{8}\)
\(=\dfrac{4\times5}{5\times8}\)
\(=\dfrac{4}{8}\)
\(=\dfrac{1}{2}\)
d) \(\dfrac{1}{2}:\dfrac{2}{5}\)
\(=\dfrac{1}{2}\times\dfrac{5}{2}\)
\(=\dfrac{1\times5}{2\times2}\)
\(=\dfrac{5}{4}\)
a) 7/15 + 4/5 = 7/15 + 12/15 = 19/15
b) 2/3 - 3/8 = 16/24 - 9/24 = 7/24
c) 4/5 × 5/8 = 4/8 = 1/2
d) 1/2 : 2/5 = 1/2 × 5/2 = 5/4
