Can you solve this .I am unable to solve ..........

This question, in fact, is a very simple question

It has been made in this style to decieve students

 

It is saying what is the total number of ways of selecting 10 balls from a bag with balls of 3 different colours

 

or

 

We can say what are the possible colour arrangements for 10 balls randomly taken out of the bag which is 10 choose 3 = 120

 

See here all balls (except different colours) are identical so 

just think there are x1 number of white balls chosen, x2 red balls & x3 blue balls.

so x1 + x2 + x3 = 10

now if you don’t know Binomial theorem it is impossible to solve this question for now. I will recommend you study it first before solving these type of questions ...anyways let's move on to the solution

here n=10, r=3,

to find the number of ways you have to find the coefficient of x^n in [ {( x^0 ) + ( x^1 ) + ( x^2 ) upto infinity } r times multiplied]

From there you will find the coefficient of x^n or x^10

is    12C2 or 12 Choose 2 = 66 (Ans)

 

Hope it helps!