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Bài 1:
\(\frac{3}{5}+\frac{4}{15}=\frac{9}{15}+\frac{4}{15}=\frac{13}{15}\)
\(\frac{5}{6}:\frac{-7}{12}=\frac{5}{6}.\frac{-12}{7}=\frac{-60}{42}=\frac{-10}{7}\)
\(\frac{-21}{24}:\frac{-14}{8}=\frac{-21}{24}.\frac{-8}{14}=\frac{168}{336}=\frac{1}{2}\)
\(\frac{4}{5}:\frac{-8}{15}=\frac{4}{5}.\frac{-15}{8}=\frac{-60}{40}=\frac{-3}{2}\)
\(\frac{5}{12}-\frac{-7}{6}=\frac{5}{12}+\frac{7}{6}=\frac{5}{12}+\frac{14}{12}=\frac{19}{12}\)
\(\frac{-15}{16}.\frac{8}{25}=\frac{-120}{400}=\frac{-3}{10}\)
Bài 2 :
\(6\frac{4}{5}-\left(1\frac{2}{3}+3\frac{4}{5}\right)\)
\(=\frac{34}{5}-\left(\frac{5}{3}+\frac{19}{5}\right)\)
\(=\frac{34}{5}-\frac{5}{3}-\frac{19}{5}\)
\(=\left(\frac{34}{5}-\frac{19}{5}\right)-\frac{5}{3}\)
\(=3-\frac{5}{3}\)
\(=\frac{4}{3}\)
\(6\frac{5}{7}-\left(1\frac{2}{3}+2\frac{5}{7}\right)\)
\(=\frac{47}{7}-\left(\frac{5}{3}+\frac{19}{7}\right)\)
\(=\frac{47}{7}-\frac{5}{3}-\frac{19}{7}\)
\(=\left(\frac{47}{7}-\frac{19}{7}\right)-\frac{5}{3}\)
\(=4-\frac{5}{3}\)
\(=\frac{7}{3}\)
\(\frac{4}{19}.\frac{-3}{7}+\frac{-3}{7}.\frac{15}{19}+\frac{5}{7}\)
\(=\left(\frac{4}{19}+\frac{15}{19}\right).\frac{-3}{7}+\frac{5}{7}\)
\(=1.\frac{-3}{7}+\frac{5}{7}\)
\(=\frac{-3}{7}+\frac{5}{7}\)
\(=\frac{2}{7}\)
\(\frac{5}{9}.\frac{7}{13}+\frac{5}{9}.\frac{9}{13}-\frac{5}{9}.\frac{3}{13}\)
\(=\frac{5}{9}.\left(\frac{7}{13}+\frac{9}{13}-\frac{3}{13}\right)\)
\(=\frac{5}{9}.1\)
\(=\frac{5}{9}\)
a) \(\frac{113}{13}-\frac{24}{7}-\frac{53}{13}=\frac{60}{13}-\frac{24}{7}\)
=\(\frac{420-312}{91}=\frac{108}{91}\)
b) \(\frac{2}{7}.\left(\frac{51}{4}-\frac{31}{4}\right)=\frac{2}{7}.5=\frac{10}{7}\)
c) \(\frac{3}{5}+1-\frac{1}{20}\)= \(\frac{12}{20}+\frac{20}{20}-\frac{1}{20}=\frac{31}{20}\)
*tính nhanh
=1*27*25*3+27*25-25*11
=25*(1*27*3+27-11)
=25*97=2425
mình chỉ làm được ý thôi nhá
a)1200
b)4905
c) Mình nghĩ là bằng 0 nếu ở thừa số thứ 2 dấu''+'' là dấu''-''
Còn nếu là dấu''+'' thì mình chịu
a) \(\frac{3}{8}+\frac{7}{12}+\frac{10}{16}+\frac{10}{24}\)
= \(\frac{3}{8}+\frac{7}{12}+\frac{5}{8}+\frac{5}{12}\)
=\(\left(\frac{3}{8}+\frac{5}{8}\right)+\left(\frac{7}{12}+\frac{5}{12}\right)\)
= \(\frac{8}{8}+\frac{12}{12}\)
= \(1+1\)
=\(2\)
b) \(\frac{4}{6}+\frac{7}{13}+\frac{17}{9}+\frac{19}{13}+\frac{1}{9}+\frac{14}{6}\)
= \(\frac{2}{3}+\frac{7}{13}+\frac{17}{9}+\frac{19}{13}+\frac{1}{9}+\frac{7}{3}\)
= \(\left(\frac{2}{3}+\frac{7}{3}\right)+\left(\frac{7}{13}+\frac{19}{13}\right)+\left(\frac{17}{9}+\frac{1}{9}\right)\)
= \(\frac{9}{3}+\frac{26}{13}+\frac{18}{9}\)
= \(3+2+2\)
= \(7\)
Chúc bạn học tốt
Tính nhanh:
a, 3/8 + 7/12 + 10/16 + 10/24
= (3/8 + 10/16) + (7/12 + 10/24)
= (6/16 + 10/16) + (14/24 + 10/24)
= 16/16 + 24/24
= 1 + 1 = 2.
b, 4/6 + 7/13 + 17/9 + 19/13 + 1/9 + 14/6
= (4/6 + 14/6) + (7/13 + 19/13) + (17/9 + 1/9)
= 18/6 + 26/13 + 18/9
= 3 + 2 + 2 = 7.
Thực hiện phép tính
-a) -5/7.7/10-3/11:6/5
b) 5/14.1/3.-4/15:5/7
c) 2 13/15.11/15-13/15+2 13/15 . 4/15
a) -5/7.7/10 - 3/11 : 6/5
= -1/2 - 5/22
= -8/11
b) 5/14.1/3.-4/15:5/7
= -2/63:5/7 = -2/45
c) 2 13/15.11/15 - 13/15 + 2 13/15.4/15
= 2 13/15.(11/15 + 4/15) - 13/15
= 2 13/15.1 - 13/15
= 2 13/15 - 13/15
= 2