Question

Știind că a/b = 7/8 aflați 3a+4b/5b-4a​

Answer 1

a/b=7/8
=> a=7
=> b=8
--------------
3a= 7•3=21
4b=8•4=32
--------------
5b=8•5=40
4a=7•4=24
---------------
21/32
---------= ?
40/24

Answer 2

Răspuns:

53/12

Explicație pas cu pas:

a/b = 7/8 => a = 7b/8

(3a+4b)/(5b-4a) = (3·7b/8 +4b)/(5b-4·7b/8) =

= (21b/8 + ⁸⁾4b) / (²⁾5b - 7b/2) = (21b+32b)/8 : (10b-7b)/2 =

= 53b/8 · 2/3b = 53/12