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afla nr a b c stiind ca a:2=b b:2=c iar a-c=21

Răspuns :

a:2=b=>a=2b
a-c=21
2b-b/2=21
4b-b=42
3b=42
b=42:3
b=14

a=2b=2*14=28

c=b/2=14/2=7