just now bothered to check the cbse book

yes it shld be just 0.9 only

the 13 th one is staight bayes thrm

the 14 th one is very simple

 

just list out the cases

 

cases                                             no of posibilities  

all four zeros                                                   1

 i one and three zeros                                      4!/ 3!=4

2 ones and two zeros                                      4!/ 2! 2!=6

three one sand one zero                                   4 possibilties again

all four ones                                                     1 again

 

therefore toral cases=16

 

no of fav cases for mod to exist

 

1   0                        or               1 0      or               1 1

0   1                                          1 1                        0 1

 

 

therefore no of fav cases=3

 

hence 3/16