Question

doi frati au impreuna 210 alune. cate alune are fiecare baiat daca unul are 2pe 5 din cantitatea celuilalt. (dau 99 de puncte :D)

Answer 1

a=primul copil
b= al doilea copil
a+b=210
a=2/5 din b
2/5 din b +b=210 (amplificam b cu 5) 
2b/5 + 5b/5 = 210
7b/5=210
7b=210*5
7b=1050
b=150 ( Al doilea copil are 150 de alune)
a=210-15
a=60 ( Primul copil are 60 de alune)

Answer 2

$x+y=210 \\ x=\frac{2}{5} \ din \ y\\ x=\frac{2y}{5} \\ \frac{2y}{5}+y=\frac{2y}{5}+\frac{5y}{5}=210 \\ \frac{7y}{5}=210 \\ 7y=210 \cdot 5 \\ 7y=1 \0 50 \\ y=\frac{1 \ 050}{7} \\ \Rightarrow\boxed{\bold{y=150 \ alune}} \\ x=\frac{2 \cdot y}{5}=\frac{2 \cdot 150}{5} \\ x=\frac{300}{5} \\ \Rightarrow \boxed{\bold{x=60 \ alune}}$