Đáp án: $\dfrac{32}{651}$
Giải thích các bước giải:
$\dfrac{5}{12.17}+\dfrac{35}{17.18}-\dfrac{39}{18.21}+\dfrac{30}{31.72}\\=\dfrac{5}{204}+\dfrac{35}{306}-\dfrac{13}{6.21}+\dfrac{5}{31.12}\\=\dfrac{5}{204}+\dfrac{35}{306}-\dfrac{13}{126}+\dfrac{5}{372}\\=\dfrac{3255+15190-13702+1785}{132804}\\=\dfrac{6528}{132804}=\dfrac{32}{651}$