Probability

see we have to have A occuring p times ..... and every time P is carries out its independent of the previous results .......

also we can select the times we want a to occur outta the n times ....

and the remainin trials have to be all givin b as result ,,,

so we have ...

nCp (x)^p (y)^(n-p) ,.....

thx :)

i had trble understanding the nCp part ..