question_answer

If there are n independent trials, p and q the probability of success and failure respectively, then probability of exactly r successes or Let p be the probability of happening an event and q its failure, then the total chance of r successes in n trials is [MP PET 1999]

A)                 \[^{n}{{C}_{n+r}}{{p}^{r}}{{q}^{n-r}}\]             

B)                 \[^{n}{{C}_{r}}{{p}^{r-1}}{{q}^{r+1}}\]

C)                 \[^{n}{{C}_{r}}{{q}^{n-r}}{{p}^{r}}\]   

D)                 \[^{n}{{C}_{r}}{{p}^{r+1}}{{q}^{r-1}}\]