求学霸解答,对了给采纳,第四题
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ADF =(1*4)/(1+2)(4+3) = 4/21
BDE =(2*2)/(1+1)(2+3) = 4/15
CEF =(3*3)/(2+3)*(3+4) = 9/35
DEF = 1 - 4/21 - 4/15 - 9/35
=17/21 - 4/15 -9/35
=(17*25-4*35-9*15)/21*25
=150/21*25
=6/21
=2/7
BDE =(2*2)/(1+1)(2+3) = 4/15
CEF =(3*3)/(2+3)*(3+4) = 9/35
DEF = 1 - 4/21 - 4/15 - 9/35
=17/21 - 4/15 -9/35
=(17*25-4*35-9*15)/21*25
=150/21*25
=6/21
=2/7
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