There are 1000 sealed envelops in a box, 10 of them contain a cash prize of 100 each, 100 of them contain a cash prize of 50 each and 200 of them contain a cash prize of 10 each and rest do not contain any cash prize. If they are well shuffled and an envelope is picket up out, What is the probability that it contains no cash prize?

Explanation

Total number of sealed envelopes in a box, n(S)=1000
Number of evelopes containing cash prize=10+100+200=310
Number of envelops containing no cash prize,
`n(E )=1000-310=690`
`P(E )=(n(E ))/(n(S))=(690)/(1000)=(69)/(100)=0.69`