Bài 1: a. 16/20-15/25 b. -5+ -2/7 c. 27/35-1 Bài 2: a. 3/8+ -5/8-1/8 b. 3/4- -1/2+1/6 c. -4/10+15/25+ -2/15 d. -7/12+ -4/30- -1/6

Đáp án:

Giải thích các bước giải:

 B1:

a)

$\dfrac{16}{20}$-$\dfrac{15}{25}$

=$\dfrac{4}{5}$-$\dfrac{3}{5}$

=$\dfrac{1}{5}$

b)

-5+$\dfrac{-2}{7}$

=$\dfrac{-5×7+(-2)}{7}$

=$\dfrac{-37}{7}$

c)

$\dfrac{27}{35}$-1

=$\dfrac{-8}{35}$

B2

a)

$\dfrac{3}{8}$+$\dfrac{-5}{8}$-$\dfrac{1}{8}$

=$\dfrac{3}{8}$+$\dfrac{-3}{4}$

=$\dfrac{-3}{8}$

b)

$\dfrac{3}{4}$-$\dfrac{-1}{2}$+$\dfrac{1}{6}$

=$\dfrac{5}{4}$+$\dfrac{1}{6}$

=$\dfrac{17}{12}$

c)

$\dfrac{-2}{5}$+$\dfrac{3}{5}$+$\dfrac{-2}{15}$

=$\dfrac{-6}{15}$+$\dfrac{9}{15}$+$\dfrac{-2}{15}$

=$\dfrac{1}{15}$

d)

$\dfrac{-7}{12}$+$\dfrac{-4}{30}$-$\dfrac{-1}{6}$

=$\dfrac{-7}{12}$+$\dfrac{-2}{15}$-$\dfrac{-1}{6}$

=$\dfrac{-11}{20}$

@maihonganh