related to probability

Question

1) An urn contains 5 red balls and 6 blue balls. A ball is drawn randomly, its colour is noted, and then the ball is replaced in the urn. If this process is repeated four times:  

i) What is the probability of getting two red balls and 2 blue balls? 

ii) What is the probability that all 4 balls are of the same colour? 

iii) What is the probability that the first red ball is drawn in the 4th trial? 

2) Number plates in an Arab country consist of 3 letters (chosen from a specified set of 20 letters from the Arabic alphabet) and 4 digits (from 0 to 9). 

i) Find the probability of a plate having identical letters. 

ii) Find the probability of a plate having identical digits. 

iii) Find the probability of a plate having consecutive digits. 

Answer 1

Hi Syed A.,

Since order of results doesn't matter, the answers requested are Combinations of results. You can look up forms for combination calculations -- they'll look like: (n!) / ((m!)*(r!)) . Study those and apply them.

--Cheers, --Mr. d.