Răspuns:35
Explicație pas cu pas:
a=suma cheltuita in prima zi,b=suma cheluia in a 2 a zi
c=suma cheltuita in a 3 a zi,x=suma totala
a=2/5x+5
b=1/4·(3/5x-5)+1,5
c=10,5
c=x-(2/5x+5)-[1/4·(3/5x-5)+1,5]
x-2/5x-5-3/20x+5/4-1,5=10,5
(20x-8x-3x)/20-21/4=10,5
(9x-105)/20=10,5
9x-105=210
9x=315
x=35
