Question

有红白黑三种颜色的球,白球和红球共15个,红球和黑球共18个,黑球和白球共9个.问三种球各多少个?

Answer 1

(白+红)=15;

(红+黑)=18;

(黑+白)=9;

所以:

(白+红)+(红+黑)-(黑+白)=2个(红)=15+18-9=24,

所以:

(红)=12;

(白)=3;

(黑)=6.