Răspuns:
a = 12,(5) = (125-12)/9=113/9
b = 9,(6) = (96-9)/9 = 87/9
a+b+c = 113/9 + 87/9 + c
a+b+c = 200/9 + c
ma = 20 1/3 = (20×3+1)/3 = 61/3
ma = (a+b+c)/3
61/3=(a+b+c)/3
61=a+b+,c
61=200/9 + c
61×9 = 200 + 9 × c
549 = 200 + 9 × c
9 × c = 549 - 200
9 × c = 349
c = 349/9
c = 38,(7)
