a) Ta có: BCNN(15,10) = 30 nên ta chọn mẫu số chung là 30

\(\frac{11}{15}+\frac{9}{10}=\frac{22}{30}+\frac{27}{30}=\frac{49}{30}\)

b) Ta có: BCNN(6,9,12) = 36 nên ta chọn mẫu số chung là 36

\(\frac{5}{6} + \frac{7}{9} + \frac{{11}}{{12}} = \frac{{30}}{{36}} + \frac{{28}}{{36}} + \frac{{33}}{{36}} = \frac{{91}}{{36}}\)

c) Ta có: BCNN(24,21) = 168 nên ta chọn mẫu số chung là 168

\(\frac{7}{{24}} - \frac{2}{{21}} = \frac{{49}}{{168}} - \frac{{16}}{{168}} = \frac{{33}}{{168}}=\frac{11}{56}\)

d) Ta có: BCNN(36,24) = 72 nên ta chọn mẫu số chung là 72

\(\frac{{11}}{{36}} - \frac{7}{{24}} = \frac{{22}}{{72}} - \frac{{21}}{{72}} = \frac{1}{{72}}\)

Trả lời

\(A=\frac{7}{12}+\frac{5}{12}\div6-\frac{11}{36}\)

\(A=\frac{7}{12}+\frac{5}{12}\times\frac{1}{6}-\frac{11}{36}\)

\(A=\frac{7}{12}+\frac{5}{72}-\frac{11}{36}\)

\(A=\frac{25}{72}\)

    \(B=12\frac{1}{3}-\frac{5}{7}\div\left(24-23\frac{5}{7}\right)\)

\(B=\frac{37}{3}-\frac{5}{7}\div\left(24-\frac{166}{7}\right)\)

\(B=\frac{37}{3}-\frac{5}{7}\div\frac{2}{7}\)

\(B=\frac{37}{3}-\frac{5}{7}\times\frac{7}{2}\)

\(B=\frac{37}{3}-\frac{5}{2}\)

\(B=\frac{59}{6}\)

Bài làm:

Ta có: 

\(A=\frac{7}{12}+\frac{5}{12}\div6-\frac{11}{36}\)

\(A=\frac{7}{12}+\frac{5}{72}-\frac{11}{36}\)

\(A=\frac{42+5-22}{72}=\frac{25}{72}\)

và

\(B=12\frac{1}{3}-\frac{5}{7}\div\left(24-23\frac{5}{7}\right)\)

\(B=\frac{37}{3}-\frac{5}{7}\div\left(24-23-\frac{5}{7}\right)\)

\(B=\frac{37}{3}-\frac{5}{7}\div\left(1-\frac{5}{7}\right)\)

\(B=\frac{37}{3}-\frac{5}{7}+1\)

\(B=\frac{265}{21}\)

\(A=\frac{7}{12}+\frac{5}{12}\div6-\frac{11}{36}\)

\(=\frac{7}{12}+\frac{5}{72}-\frac{11}{36}\)

\(=\frac{42}{72}+\frac{5}{72}-\frac{22}{72}\)

\(=\frac{25}{72}\)

\(B=12\frac{1}{3}-\frac{5}{7}\div(24-23\frac{5}{7})\)

\(=12\frac{1}{3}-\frac{5}{7}\div(24-23-\frac{5}{7})\)

\(=12\frac{1}{3}-\frac{5}{7}\div(1-\frac{5}{7})\)

\(=\frac{37}{3}-\frac{5}{7}\div\frac{2}{7}\)

\(=\frac{37}{3}-\frac{5}{2}\)

\(=\frac{74}{6}-\frac{15}{6}\)

\(=\frac{59}{6}\)

Chúc bạn học tốt

\(A=\frac{7}{12}+\frac{5}{12}:6-\frac{1}{36}\)

\(=\frac{7}{12}+\frac{5}{72}-\frac{11}{36}\)

\(=\frac{42}{72}+\frac{5}{72}-\frac{22}{72}\)

\(=\frac{25}{72}\)

A=25/72\

B=59/6

\(B=12\frac{1}{3}-\frac{5}{7}:\left(24-23\frac{5}{7}\right)\)

\(=\frac{37}{3}-\frac{5}{7}:\left(1-\frac{5}{7}\right)\)

\(=\frac{37}{3}-\frac{5}{7}:\frac{2}{7}\)

\(=\frac{37}{3}-\frac{5}{2}\)

\(=\frac{59}{6}\)

Bài 1:

a) Ta có: \(\frac{8}{40}+\frac{-4}{20}-\frac{3}{5}\)

\(=\frac{1}{5}+\frac{-1}{5}-\frac{3}{5}\)

\(=\frac{-3}{5}\)

b) Ta có: \(\frac{-7}{12}+\frac{-2}{12}-\frac{-3}{36}\)

\(=\frac{-7}{12}+\frac{-2}{12}-\frac{-1}{12}\)

\(=\frac{-9+1}{12}=\frac{-8}{12}=\frac{-2}{3}\)

c) Ta có: \(\left(\frac{1}{6}+\frac{-4}{13}\right)-\left(-\frac{17}{6}-\frac{30}{13}\right)\)

\(=\frac{1}{6}+\frac{-4}{13}+\frac{17}{6}+\frac{30}{13}\)

\(=3+2=5\)

d) Ta có: \(-\frac{-5}{4}+\frac{7}{4}-\frac{-11}{7}+\frac{2}{7}\)

\(=\frac{5}{4}+\frac{7}{4}+\frac{11}{7}+\frac{2}{7}\)

\(=3+\frac{13}{7}=\frac{21}{7}+\frac{13}{7}=\frac{34}{7}\)

e) Ta có: \(-\frac{1}{8}+\frac{-7}{9}+\frac{-7}{8}+\frac{6}{7}+\frac{2}{14}\)

\(=-1+1+\frac{-7}{9}\)

\(=-\frac{7}{9}\)

f) Ta có: \(\frac{-2}{9}-\frac{11}{-9}+\frac{5}{7}-\frac{-6}{-7}\)

\(=\frac{-2-\left(-11\right)}{9}+\frac{5-6}{7}\)

\(=1+\frac{-1}{7}=\frac{7}{7}+\frac{-1}{7}=\frac{6}{7}\)

\(a,\frac{7}{12}\cdot\frac{6}{11}+\frac{7}{12}\cdot\frac{5}{11}+2\frac{7}{12}\)

\(=\frac{7}{12}\cdot\left(\frac{6}{11}+\frac{5}{11}\right)+2\frac{7}{12}\)

\(=\frac{7}{12}+\frac{31}{12}\)

\(=\frac{38}{12}=\frac{19}{6}\)

\(b,\frac{-5}{9}\cdot\frac{-6}{13}+\frac{5}{-9}\cdot\frac{-5}{13}-\frac{5}{9}\)

\(=\frac{-5}{9}\cdot\frac{-6}{13}+\frac{-5}{9}\cdot\frac{-5}{13}+\frac{-5}{9}\cdot1\)

\(=\frac{-5}{9}\cdot\left(\frac{-6}{13}+\frac{-5}{13}+1\right)\)

\(=\frac{-5}{9}\cdot\left(\frac{-11}{13}+1\right)\)

\(=\frac{-5}{9}\cdot\frac{2}{13}\)

\(=\frac{-10}{117}\)

\(c,\)\(0,8\cdot\frac{-15}{14}-\frac{4}{5}\cdot\frac{13}{14}-1\frac{2}{5}\)

\(=\frac{4}{5}\cdot\frac{-15}{14}-\frac{4}{5}\cdot\frac{13}{14}-\frac{7}{5}\)

\(=\frac{4}{5}\cdot\left(\frac{-15}{14}-\frac{13}{14}\right)-\frac{7}{5}\)

\(=\frac{4}{5}\cdot\left(-2\right)-\frac{7}{5}\)

\(=\frac{-8}{5}-\frac{7}{5}\)

\(=-3\)

\(d,\)\(75\%\cdot\frac{6}{7}+5\%\cdot\frac{6}{7}+\frac{7}{10}\cdot1\frac{1}{7}\)

\(=\frac{3}{4}\cdot\frac{6}{7}+\frac{1}{20}\cdot\frac{6}{7}+\frac{7}{10}\cdot\frac{8}{7}\)

\(=\left(\frac{3}{4}+\frac{1}{20}\right)\cdot\frac{6}{7}+\frac{7}{10}\cdot\frac{8}{7}\)

\(=\frac{4}{5}\cdot\frac{6}{7}+\frac{4}{5}\cdot1\)

\(=\frac{4}{5}\cdot\left(\frac{6}{7}+1\right)\)

\(=\frac{4}{5}\cdot\frac{13}{7}\)

\(=\frac{52}{35}\)

a)7/12.6/11+7/12.5/11-2.7/12

=7/12(6/11+5/11-2)

=7/12(1-2)

=7/12.(-1)

=-7/12

a . 7/12 . 6/11 + 7/12 . 5/11 - 2 7/12

= 7/12 . ( 6/11 + 5/11 ) - 31/12

= 7/12 . 1 - 31/12

= 7/12 - 31/12

= -2

b . -5/9 . -6/13 + 5/-9 . -5/13 - 5/9

= -5/9 . ( -6/13 + -5/13 ) - 5/9

= -5/9 . ( -1 ) -5/9

= 5/9 - 5/9

= 0

\(\frac{25}{12}.\frac{23}{7}-\frac{25}{12}.\frac{12}{7}\)

\(=\frac{25}{12}.\left(\frac{23}{7}-\frac{12}{7}\right)\)\(\)

\(=\frac{25}{12}.\frac{11}{7}\)

\(=\frac{275}{84}\)

\(-\frac{6}{7}.\frac{7}{10}.\frac{11}{-6}.\left(-20\right)\)

\(=-\frac{3}{5}.\frac{-11}{6}.\left(-20\right)\)

\(=\frac{11}{10}.\left(-20\right)\)

\(=-22\)

Tính

\(\frac{12}{25}.\frac{23}{7}-\frac{12}{25}.\frac{12}{7}=\frac{12}{25}\left(\frac{23}{7}-\frac{12}{7}\right)\)

                                         \(=\frac{12}{25}.\frac{11}{7}=\frac{132}{175}\)

\(-\frac{6}{11}.\frac{7}{10}.\frac{11}{-6}.\left(-20\right)\)

\(=\frac{-6.7.11.\left(-20\right)}{11.10.\left(-6\right)}=7.\left(-20\right)=-140\)

Sửa lại câu thứ 2 :vv

\(-\frac{6}{11}.\frac{7}{10}.\frac{11}{6}.\left(-20\right)=\frac{-6.7.11.\left(-20\right)}{11.10.6}=7.\left(-2\right)=-14\)