Question

Daca avem proportia a pe 5 = 8 pe b stabiliti valoarea diferentei ab-13

Answer 1

a/5=8/b

ab=5*8
ab=40

Deci 
40-13=27

Answer 2

$\frac{a}{5}= \frac{8}{b} \Rightarrow ab=5 \cdot 8 \Leftrightarrow ab=40. \\ \\ \boxed{ab-13=40-13=\boxed{27}}$