1-(49*13+23*49)
=1-4/9*(1/3+2/3)
=1-4/9
=5/9
2.8*(17+328)
=2.8*1/7+2.8*3/28
=0.4+0.3
=0.7
101*99102
=(102-1)*99/102
=99-99/102
=98又3/102
=98又1/34
1-(49*13+23*49)
=1-4/9*(1/3+2/3)
=1-4/9
=5/9
2.8*(17+328)
=2.8*1/7+2.8*3/28
=0.4+0.3
=0.7
101*99102
=(102-1)*99/102
=99-99/102
=98又3/102
=98又1/34