还是概率,数学英文都好的进a calculator manufacturer checks for defective

还是概率,数学英文都好的进
a calculator manufacturer checks for defective products by testing 3 calculators out of every lot of 12.if a defective calculator is found,the lot is rejected.
a.suppose 2 calculators in a lot are defective.calculate the probability that the lot will be rejected
b.the quality-control department wants to have at least a 30% chance of rejecting lots that contain only one defective calculator.is calculators in a lot of 12 sufficient?if not why and how to promote.suppose answer with mathematical calculations
第一问我就用,1减去（2选0）乘（10选3）除与（12选3）
第2问.我不太明白究竟要怎么做.达人们给点提示,思路是什么样的
第一问是没什么问题了。
第二问。你的思路是什么样的呢。给说说吧