1. Rút gọn các phân số:
\(\eqalign{
& {{21} \over 8} = ...\,\,\,\,\,\,\,\,\,\,{9 \over {36}} = ... \cr
& {{18} \over {54}} = ...\,\,\,\,\,\,\,\,\,\,{{30} \over {48}} = ... \cr
& {{90} \over {72}} = ...\,\,\,\,\,\,\,\,\,\,{{72} \over {42}} = ... \cr} \)
2. Khoanh vào những phân số bằng \({3 \over 4}\):
\({9 \over {12}}\,\,\,\,\,\,\,\,\,{{15} \over {16}}\,\,\,\,\,\,\,\,\,\,\,{{15} \over {20}}\,\,\,\,\,\,\,\,\,\,\,{{18} \over {25}}\,\,\,\,\,\,\,\,\,\,\,\,\,{{18} \over {24}}\)
3. Khoanh vào những phân số bằng \({{25} \over {100}}\):
\({5 \over {20}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,{{15} \over {65}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{3 \over {12}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{8 \over 2}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{{20} \over {80}}\)
4. Tính theo mẫu:
Mẫu: 
a) \({{2 \times 5 \times 11} \over {3 \times 11 \times 5}} = ....\)
b) \({{8 \times 12 \times 17} \over {19 \times 12 \times 8}} = ...\)
c) \({{6 \times 9 \times 11} \over {11 \times 9 \times 12}} = .....\)
5. Đúng ghi Đ, sai ghi S:
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1.
\(\eqalign{
& {{21} \over 8} = {3 \over 4}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{9 \over {36}} = {1 \over 4} \cr
& {{18} \over {54}} = {1 \over 3}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{{30} \over {48}} = {5 \over 8} \cr
& {{90} \over {72}} = {5 \over 4}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{{72} \over {42}} = {{12} \over 7} \cr} \)
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