a+b/2 =3.1/8 ; a+b /2 =25/8 ; 8(a+b )=2*25 ; 8a+8b =50
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a =1.1/2 ; a =3/2
8*3 /2 + 8b = 50 numitor 2
24+16b =100
16b =200-24
16b =76
b =76/16 = 19/4
verif ;3/2+19/4 6/4+19/4 25 1 25
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