Salut,
1. a/b = 3/5 → a = 3b/5.
a+b = 240
3b/5+b = 240
3b+5b = 1200
8b = 1200
b = 1200/8
b = 150.
a = 3b/5
a = 3•150/5
a = 3•30
a = 90.
2. 360+20% din 360 = 360+20/100•360 = 360+2•36 = 360+72 = 432 lei după scumpire.
3. considerăm x, y, z → unghiurile ∆ABC :
{x;y;z} dp {4;5;9}.
x/4 = y/5 =z/9 = k
x/4 = k → x = 4k.
y/5 = k → y = 5k.
z/9 = k → z = 9k.
x+y+z = 180
4k+5k+9k = 180
18k = 180
k = 180/18
k = 10.
x = 4•10 → x = 40
y = 5•10 → y = 50
z = 9•10 → z = 90.
Succes! :3