1. daca x / y = 5 / 7 atunci x / 5 = y / 7 = k
x = 5k
y = 7k
( 3x + 2y ) / ( x + 4y ) = ( 3 · 5k + 2 ·7k ) / ( 5k + 4 ·7k) = 29k / 33k =
29 /33
2. daca a / b = 9 /10 atunci a / 9 = b / 10 = k
a = 9k
b = 10k ⇒ ( 7 ·9k - 10k) / ( 9k + 10k ) = 53k / 19k = 53 / 19
3. daca x / y = 4 / 9 atunci x/ 4 = y / 9 = k
x = 4k
y = 9k ( 3 · 4k - 9k) / ( 2 ·4k - 4 ·9k) = 3k / ( - 28k) = - 3 / 28