Question

doi prieteni au impreuna 400 lei. Daca primul i-ar da celuilalt 80 lei, atunci el ar avea o suma de 4 ori mai mica decat cel de al doilea. Cati lei avea primul?

Answer 1

a+b = 400
a-80 = (b+80):4
4×(a-80) = b+80
4×a-320 = b+80
4×a = b+80+320
4×a = b+400 => b = 4×a-400
a |____|
b |____|____|____|____| -400
avem 5 segmente egale -400 = 400
400 + 400 = 800
800 : 5 = 160 ( un segment)
a = 160
b = 4×160-400 = 640-400 = 240

Verificare:
160+240 = 400
160-80 = (240+80):4
80 = 320:4
80 = 80

a = 160
b = 240