Bài tập 1 trang 75 VBT Toán 4 tập 2

a) \(\displaystyle {5 \over 8} + {9 \over {32}} = {{20} \over {32}} + {9 \over {32}} = {{29} \over {32}}\) 

b) \(\displaystyle {4 \over 5} - {4 \over 7} = {{28} \over {35}} - {{20} \over {35}} = {8 \over {35}}\)

c) \(\displaystyle {9 \over {14}} \times {7 \over 6} = {{9 \times 7} \over {14 \times 6}} \)\(\displaystyle= {{3\times 3 \times 7} \over {7\times 2 \times 3 \times 2}}= {3 \over 4}\)

d) \(\displaystyle {5 \over 9}:{{10} \over {21}} = {5 \over 9} \times {{21} \over {10}} = {{5 \times 21} \over {9 \times 10}} \)\(\displaystyle= {{5\times 3 \times 7} \over {3\times 3 \times 5 \times 2}} ={7 \over 6}\)

e) \(\displaystyle {8 \over {15}} + {4 \over {15}}:{2 \over 5} = {8 \over {15}} + {4 \over {15}} \times {5 \over 2}\)

\(\displaystyle = {8 \over {15}} + {2 \over 3} = {{8 } \over {15}}+ {10 \over 15} = {{18} \over {15}} = {6 \over 5}\)

-- Mod Toán lớp 4 HỌC247