Giải câu 4 trang 44 toán 6 tập 1 sgk chân trời sáng tạo.
a) Ta có: BCNN(15, 10) = 30
30 : 10 = 3; 30 : 15 = 2
=> $\frac{11}{15}$ + $\frac{9}{10}$
= $\frac{11 . 2}{15 . 2}$ + $\frac{9 . 3}{10 . 3}$
= $\frac{22}{30}$ + $\frac{27}{30}$
= $\frac{49}{30}$.
b) Ta có: BCNN(6, 9, 12) = 36
36 : 6 = 6; 36 : 9 = 4; 36 : 12 = 3
=> $\frac{5}{6}$ + $\frac{7}{9}$ + $\frac{11}{12}$
= $\frac{5 . 6}{6 . 6}$ + $\frac{7 . 4}{9 . 4}$ + $\frac{11 . 3}{12 . 3}$
= $\frac{30}{36}$ + $\frac{28}{36}$ + $\frac{33}{36}$;
= $\frac{91}{36}$.
c) Ta có: BCNN(21, 24) = 168
168 : 21 = 8; 168 : 24 = 7
=> $\frac{7}{24}$ - $\frac{2}{21}$
= $\frac{7 . 7}{24 . 7}$ - $\frac{2 . 8}{21 . 8}$
= $\frac{49}{168}$ - $\frac{16}{168}$
= $\frac{33}{168}$
= $\frac{11}{56}$.
d) Ta có: BCNN(36, 24) = 72
72 : 36 = 2; 72 : 24 = 3
=> $\frac{11}{36}$ - $\frac{7}{24}$
= $\frac{11 . 2}{36 . 2}$ - $\frac{7 . 3}{24 . 3}$
= $\frac{22}{72}$ - $\frac{21}{72}$
= $\frac{1}{72}$.