quantskillsgmat wrote:There are 6 boxes numbered from 1 to 6.Each box is to be filled up either with red or green ball in such a way that atleast 1 box contains a green ball and boxes containing are consecutively numbered.The total number of ways in which this can be done is
a)5 b)21 c)33 d)60

The least no. of green balls can be 1.
If there is 1 green and 5 red balls, then there are 6 ways of placing them in 6 boxes.
If there are 2 green and reaming 4 red balls, then this can be done in 5 ways.
If there are 3 green and 3 red balls, then this can be done in 4 ways.
If there are 4 green and 2 red balls, then this can be done in 3 ways.
If there are 5 green and 1 red ball, then this can be done in 2 ways.
If there are 6 green and 0 red balls, then this can be done in 1 way.

So, total no. of ways = 6 + 5 + 4 + 3 + 2 + 1 = 21 ways

The correct answer is B.