Bài 1 :
$\dfrac{36}{24}$ = $\dfrac{36 : 12}{24 : 12}$ = $\dfrac{3}{2}$

$\dfrac{28}{20}$ = $\dfrac{28 : 4}{20 : 4}$ = $\dfrac{7}{5}$

$\dfrac{27}{15}$ = $\dfrac{27 : 3}{15 : 3}$ = $\dfrac{9}{5}$

$\dfrac{72}{56}$ : $\dfrac{72 : 8}{56 : 8}$ = $\dfrac{9}{7}$

$\dfrac{112}{140}$ = $\dfrac{112 : 28}{140 : 28 }$ = $\dfrac{4}{5}$

$\dfrac{39}{65}$ = $\dfrac{39 : 13}{65 : 13}$ = $\dfrac{3}{5}$

$\dfrac{117117}{504504}$ = $\dfrac{117117 : 9009}{504504 : 9009}$ = $\dfrac{13}{56}$

$\dfrac{153153}{414414}$ = $\dfrac{153153 : 9009}{414414 : 9009}$ = $\dfrac{17}{46}$

$\dfrac{3131}{3535}$ = $\dfrac{3131 : 101}{3535 : 101}$ = $\dfrac{31}{35}$

$\dfrac{414141}{494949}$ = $\dfrac{414141 : 10101}{494949 : 10101}$ = $\dfrac{41}{49}$

Bài 2 :
a, Các phân số tối giản là : $\dfrac{9}{11}$; $\dfrac{16}{23}$; $\dfrac{91}{100}$

b, Các phân số chưa tối giản là : $\dfrac{7}{14}$; $\dfrac{15}{24}$; $\dfrac{64}{80}$

c,
$\dfrac{7}{14}$ = $\dfrac{7 : 7}{14 : 7}$ = $\dfrac{1}{2}$

$\dfrac{15}{24}$ = $\dfrac{15 : 3}{24 : 3}$ = $\dfrac{5}{8}$

$\dfrac{64}{80}$ = $\dfrac{64 : 16}{80 : 16}$ = $\dfrac{4}{5}$

~ Chúc tus học tốt nhé ~