一个盒子有木珠,红色玻璃珠,蓝色玻璃珠.玻璃珠的数量是木珠的四倍.如果从盒子里随机取一个珠子,拿到红色玻璃珠的概率是蓝色的三倍.如果盒子里有12个红色玻璃珠,那么盒子一共多少珠子?
solution:
suppose the number of wood beads,red glass beads,and blue glass beads are a,b and c respectly.
we have :b+c=4a; b=3c;b=12
so :a=4,b=12,c=4,a+b+c=20
一共20个