17 votes 17 votes There are $3$ red socks, $4$ green socks and $3$ blue socks.You choose $2$ socks. The probability that they are of the same colour is $\dfrac{1}{5}$ $\dfrac{7}{30}$ $\dfrac{1}{4}$ $\dfrac{4}{15}$ Quantitative Aptitude gatecse-2017-set2 quantitative-aptitude probability + – Arjun asked Feb 14, 2017 • edited Dec 21, 2017 by pavan singh Arjun 9.0k views answer comment Share Follow See all 0 reply Please log in or register to add a comment.
Best answer 40 votes 40 votes $\large\dfrac{^{3}C_{2}+^{4}C_{2}+^{3}C_{2}}{^{10}C_{2}}=\dfrac{4}{15}.$ assuming ball are not identical Correct Answer: $D$ 2018 answered Feb 14, 2017 • edited Apr 28, 2019 by Naveen Kumar 3 2018 comment Share Follow See 1 comment See all 1 1 comment reply s_dr_13 commented Jan 28, 2020 reply Follow Share I thought of using this approach but I stuck at thinking whether or not it is valid to apply combination here ! We apply nCr When n is distinct but here it is group and within the group,the balls are distinct ( assuming) How can we apply nCr then ? 1 votes 1 votes Please log in or register to add a comment.
30 votes 30 votes P(Socks of Same Colour) = 2 Red or 2 Green or 2 Blue $ P(socks of Same Colour) = \frac{3}{10}*\frac{2}{9}+\frac{4}{10}*\frac{3}{9}+\frac{3}{10}*\frac{2}{9}\\ P(socks of Same Colour) = \frac{4}{15} $ sandeep007734 answered Feb 17, 2017 sandeep007734 comment Share Follow See all 0 reply Please log in or register to add a comment.
5 votes 5 votes 3 different kind of socks so choose 4 socks gives you pair of same color. so 4/15 Answer is d Prashant. answered Feb 14, 2017 Prashant. comment Share Follow See 1 comment See all 1 1 comment reply Rahul Garg commented Dec 19, 2017 reply Follow Share gud approch .. but why is there 15 in denominator ? 0 votes 0 votes Please log in or register to add a comment.
3 votes 3 votes Probability of selecting two socks of same colour = (3C2+4C2+3C2)/10C2=4/15 Ans: D) 4/15 Arnabi answered Feb 14, 2017 Arnabi comment Share Follow See all 0 reply Please log in or register to add a comment.