Tính :
a) \(\displaystyle {1 \over 4} + {3 \over 8} + {5 \over {16}} = .................\)
b) \(\displaystyle {3 \over 5}\, - \,{1 \over 3} - {1 \over 6} = .................\)
c) \( \displaystyle {4 \over 7} \times {5 \over 8} \times {7 \over {12}} = .................\)
d) \(\displaystyle {{25} \over {28}}:{{15} \over {14}} \times {6 \over 7} = .................\)
a) \(\displaystyle {1 \over 4} + {3 \over 8} + {5 \over {16}} = {4 \over 16} + {6 \over 16} + {5 \over {16}} =\displaystyle {{4 + 6 + 5} \over {16}} = {{15} \over {16}}\)
b) \(\displaystyle {3 \over 5}\, - \,{1 \over 3} - {1 \over 6} = {{18} \over {30}} - {{10} \over {30}} - {5 \over {30}} \displaystyle= {{18 - 10 - 5} \over {30}} ={3 \over {30}}= {1 \over {10}}\)
c)
\( \displaystyle {4 \over 7} \times {5 \over 8} \times {7 \over {12}} = {{4 \times 5 \times 7} \over {7 \times 8 \times 12}} \)\( \displaystyle ={{\not{4} \times 5 \times \not{7}} \over {\not{7} \times \not{4} \times 2 \times 12}}= {5 \over {12 \times 2}} = {5 \over {24}}\)
d)
\(\displaystyle {{25} \over {28}}:{{15} \over {14}} \times {6 \over 7} = {{25} \over {28}} \times {{14} \over {15}} \times {6 \over 7} \)\( \displaystyle = {{25 \times 14 \times 6} \over {28 \times 15 \times 7}} \)\( \displaystyle= {{5 \times \not{5} \times \not{14} \times \not{2} \times \not{3}} \over {\not{14} \times \not{2} \times \not{5} \times \not{3} \times 7}} = {5 \over 7}\)
-- Mod Toán lớp 5
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