\(\displaystyle{{3.4 + 3.7} \over {6.5 + 9}} = {{3.(4 + 7)} \over {3.(2.5 + 3)}} = {{4 + 7} \over {2.5 + 3}} \)\(\displaystyle= {{11} \over {13}}\)
\(\displaystyle{{6.9 - 2.17} \over {63.3 - 119}} = {{2.(3.9 - 17)} \over {7.(9.3 - 17)}} = {2 \over 7}\)
\(BCNN (13; 7)= 13.7 =91.\)
Quy đồng mẫu số các phân số ta có :
\(\displaystyle{{11} \over {13}} = {{11.7} \over {13.7}} = {{77} \over {91}}\;;\;\) \(\displaystyle{2 \over 7} = {{2.13} \over {7.13}} = {{26} \over {91}}\)
