Notam numarul total de bile cu x
Bilele albe = 3/5 * x
Restul de bile = x - 3/5 *x = x(1-3/5) = x(5/5-3/5) = x * 2/5
Bilele negre = 4/6 * x * 2/5 = 2/3 * x * 2/5 = x * 4/15
Restul de bile = x * 2/5 - x * 4/15 = x * 6/15 - x * 4/15 = x * 2/15
Acest rest reprezinta bilele rosii = 8, adica
x * 2/15 = 8
x = 8 : 2/15 = 8 x 15/2 = 4 x 15
x = 60, deci numarul total de bile = 60