Bài 1 trang 159 SGK Toán 5

Đề bài

Tính rồi thử lại (theo mẫu): 

a) Mẫu:     \(\begin{array}{*{20}{c}}{ - \begin{array}{*{20}{c}}{5746}\\{1962}\end{array}}\\\hline{\,\,\,\,\,3784}\end{array}\)              Thử lại:       \(\begin{array}{*{20}{c}}{ + \begin{array}{*{20}{c}}{3784}\\{1962}\end{array}}\\\hline{\,\,\,\;5746}\end{array}\)   

\(8923 - 4157\) ;                              \(27069 - 9537\) 

b) Mẫu:       \(\dfrac{8}{{11}} - \dfrac{3}{{11}} = \dfrac{5}{{11}}\)                    Thử lại:       \(\dfrac{5}{{11}} + \dfrac{3}{{11}} = \dfrac{8}{{11}}\)

\(\displaystyle {8 \over {15}} - {2 \over {15}}\) ;          \(\displaystyle {7 \over {12}} - {1 \over 6}\);          \(\displaystyle 1 - {3 \over 7}\)    

c) Mẫu:       \(\begin{array}{*{20}{c}}{ - \begin{array}{*{20}{c}}{7,254}\\{2,678}\end{array}}\\\hline{\,\,\,\,\,4,576}\end{array}\)            Thử lại:       \(\begin{array}{*{20}{c}}{ + \begin{array}{*{20}{c}}{4,576}\\{2,678}\end{array}}\\\hline{\,\,\,\;7,254}\end{array}\) 

\(7,284 - 5,596\) ;                       \(0,863 - 0,298\)

Lời giải chi tiết

a) 

\(\begin{array}{*{20}{c}}{ - \begin{array}{*{20}{c}}{8923}\\{4157}\end{array}}\\\hline{\,\,\,\,\,4766}\end{array}\)            Thử lại:       \(\begin{array}{*{20}{c}}{ + \begin{array}{*{20}{c}}{4766}\\{4157}\end{array}}\\\hline{\,\,\,\;8923}\end{array}\)

\(\begin{array}{*{20}{c}}{ - \begin{array}{*{20}{c}}{27069}\\{\;\,9537}\end{array}}\\\hline{\,\,\,\,17532}\end{array}\)         Thử lại:      \(\begin{array}{*{20}{c}}{ + \begin{array}{*{20}{c}}{17532}\\{\;\,9537}\end{array}}\\\hline{\,\,\,\,27069}\end{array}\)

b) 

+) \( \displaystyle{8 \over {15}} - {2 \over {15}} = {6 \over {15}}\)     

Thử lại:  \( \displaystyle{6 \over {15}} + {2 \over {15}} = {8 \over {15}}\)

+) \( \displaystyle{7 \over {12}} - {1 \over 6} = {7 \over {12}} - {2 \over {12}} = {5 \over {12}}\)         

Thử lại:  \( \displaystyle{5 \over {12}} + {1 \over 6} = {5 \over {12}} + {2 \over {12}} = {7 \over {12}}\)

+) \( \displaystyle1 - {3 \over 7} = {7 \over 7} - {3 \over 7} = {4 \over 7}\)                 

Thử lại:  \( \displaystyle{4 \over 7} + {3 \over 7} = {7 \over 7} = 1\)

c) 

\(\begin{array}{*{20}{c}}{ - \begin{array}{*{20}{c}}{7,284}\\{5,596}\end{array}}\\\hline{\,\,\,\,1,688}\end{array}\)          Thử lại:      \(\begin{array}{*{20}{c}}{ + \begin{array}{*{20}{c}}{1,688}\\{5,596}\end{array}}\\\hline{\,\,\,\,7,284}\end{array}\)

\(\begin{array}{*{20}{c}}{ - \begin{array}{*{20}{c}}{0,863}\\{0,298}\end{array}}\\\hline{\,\,\,\,\,0,565}\end{array}\)         Thử lại:       \(\begin{array}{*{20}{c}}{ + \begin{array}{*{20}{c}}{0,565}\\{0,298}\end{array}}\\\hline{\,\,\,\;0,863}\end{array}\)