1. Viết số thích hợp vào chỗ chấm:
\[\eqalign{a]
& {3 \over 5} = {{3 \times 2} \over {5 \times 2}} = {{...} \over {...}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{2 \over 7} = {{2 \times 3} \over {7 \times ...}} = {{...} \over {...}} \cr
& {1 \over 4} = {{1 \times ...} \over {4 \times 5}} = {{...} \over {...}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{8 \over 3} = {{8 \times ...} \over {3 \times ...}} = {{32} \over {...}} \cr
& {9 \over {12}} = {{9:3} \over {12:3}} = {{...} \over {...}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{{25} \over {35}} = {{25:...} \over {35:5}} = {{...} \over {...}} \cr
& {{21} \over {14}} = {{21:...} \over {14:7}} = {{...} \over {...}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{{56} \over {24}} = {{56:8} \over {24:...}} = {{...} \over {...}} \cr} \]
b] \[{2 \over 5} = {{...} \over {10}};\,\,\,\,\,\,\,{{12} \over {30}} = {{...} \over {10}};\,\,\,\,\,\,\,\,\,\,\,\,\,{{72} \over {45}} = {8 \over {....}};\,\,\,\,\,\,\,\,\,\,\,\,\,\,{1 \over 4} = {7 \over {....}}\]
2. Viết tiếp số thích hợp vào chỗ chấm:
a] \[{{12} \over {20}} = {6 \over {...}} = {3 \over {...}}\] b] \[{2 \over 5} = {{...} \over {10}} = {{...} \over {15}} = {{...} \over {20}}\]
c] \[{{24} \over {36}} = {8 \over {...}} = {2 \over {...}}\] d] \[{3 \over 4} = {... \over {12}} = {{...} \over {16}} = {{...} \over {20}}\]
3. Chuyển thành phép chia với các số bé hơn [theo mẫu]
Mẫu : 60 : 20 = [60 : 10 ] : [20 : 10] = 6 : 2 = 3
a] 75 : 25 = [75 : ] : [25 : 5] =
b] 90 : 18 = [90 : ] : [18 : 9] = ..
Bài giải:
1.
\[\eqalign{ a]
& {3 \over 5} = {{3 \times 2} \over {5 \times 2}} = {6 \over {10}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{2 \over 7} = {{2 \times 3} \over {7 \times 3}} = {6 \over {21}} \cr
& {1 \over 4} = {{1 \times 5} \over {4 \times 5}} = {5 \over {20}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{8 \over 3} = {{8 \times 4} \over {3 \times 4}} = {{32} \over {12}} \cr
& {9 \over {12}} = {{9:3} \over {12:3}} = {3 \over 4}\,\,\,\,\,\,\,\,\,\,\,\,\,{{25} \over {35}} = {{25:5} \over {35:5}} = {5 \over 7} \cr
& {{21} \over {14}} = {{21:7} \over {14:7}} = {3 \over 2}\,\,\,\,\,\,\,\,\,\,\,\,{{56} \over {24}} = {{56:8} \over {24:8}} = {7 \over 6} \cr} \]
b \[{2 \over 5} = {4 \over {10}};\,\,\,\,\,\,{{12} \over {30}} = {4 \over {10}};\,\,\,\,\,\,\,\,\,\,\,\,\,\,{{72} \over {45}} = {8 \over 5};\,\,\,\,\,\,\,\,\,\,\,\,\,{1 \over 4} = {7 \over {28}}\]
2.
a] \[{{12} \over {20}} = {6 \over {10}} = {3 \over 5}\] b] \[{2 \over 5} = {4 \over {10}} = {6 \over {15}} = {8 \over {20}}\]
c] \[{{24} \over {36}} = {8 \over {12}} = {2 \over 3}\] d] \[{3 \over 4} = {9 \over {12}} = {{12} \over {16}} = {{15} \over {20}}\]
3.
Mẫu : 60 : 20 = [60 : 10 ] : [20 : 10] = 6 : 2 = 3
a] 75 : 25 = [75 : 5] : [25 : 5] = 15 : 5
b] 90 : 18 = [90 : 9] : [18 : 9] = 10 : 2 = 5