已知离散型随机变量X的概率分布为
X10203040
P0.20.10.5a
(1)求常数a;(2)求X的数学期望EX.
Howcanyou_____andwatchthecountrygotoruin?
Themanageriscallingona______customertryingtotalkhimintosigningthecontract．
Johnsaysthathispresentjobdoesnotprovidehimwithenough______forhisorganizingability.
Hehasmadeanotherwonderfuldiscovery,_____ofgreatimportancetoscience.
