Question

Fie a si b doua numere direct proportionale cu 2 si 5 . Calculati 5a-b, stiind ca 3a+b=44.

Answer 1

 {a,b} d.p {2,5} ⇒ a/2 = b/5 = k

a= 2k
b=5k

3a+b=44
6k+5k= 44
11k = 44 
k = 44 : 11
k =4 ⇒ a = 2·4 = 8 
            b = 5·4 = 20

5a-b = ?
5·8 -20= 40 - 20 = 20 

Sper ca te-am ajutat !

Answer 2

{ a,b } d.p ( direct proportionale ) { 2,5 }
------------------/--------
3a + b = 44 
5a - b = ?
-----------------//---------

a / 2 = b / 5 = K

a / 2 = K => a = 2 K
b / 5 = K => b = 5 K

3 x 2 K + 5 K = 44
6 K  + 5 K = 44
11 K = 44
K = 4

a = 4 x 2 = 8

b = 4 x 5 = 20

⇒ 5a - b = 

= 5 x 8 - 20 

= 40 - 20

= 20