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calculati 7a+9b+9c+7d, stiind ca a+b+c+d=30 si a+d=10

Răspuns :

a+b+c+d=30
a+d=10
asadar, b+c=20
deci putem scriem primul enunt si ca: 7(a+d) + 9(b+c)= 7*10+9*20=70+180=250
A+b+c+d=30 Stii ca a+d=10 => 10 +b+ c=30=> b+c=20
7 (a+d) + 9 (b+c)=7×10+9×20=70+180=250