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2014-11-11T22:59:01+02:00
 \frac{a+b}{2}=15  ⇒a+b=30;
 \frac{a}{b}= \frac{1}{4}   ⇒b=4·a;
⇒a+4·a=30 ⇒ 5·a=30 ⇒a= \frac{30}{5}  ⇒ a=6 ⇒b=6·4 ⇒ b=24
18 4 18
2014-11-11T23:08:30+02:00
(a+b)/2=15 => a=30-b
a/b=1/4                      => (30-b)*4=b
120-4b=b
5b=120
b=24
a=30-b= 30-24=6

9 3 9