In the U.S., some toys,like small rubber balls, must carry warning labels.

VOA: standard.2010.02.23

But in our case, the probability of backscattering is going to be the number of balls that backscatter, and that's going to be divided by the total number of ping-pong balls.

用20除以132000，但现在背散射,的概率是被散射回来的小球，除以总的小球数,你们记得。

麻省理工公开课 - 化学原理课程节选

But in our case, the probability of backscattering is going to be the number of balls that backscatter, and that's going to be divided by the total number of ping-pong balls.

用20除以132000，但现在背散射,的概率是被散射回来的小球，除以总的小球数,你们记得。

麻省理工公开课 - 化学原理课程节选