Answer
Verified
416.7k+ views
Hint: First see what are the total no. of students in the class and how many are to be taken randomly out. For selecting we use a combination formula as \[{}^{n}{C_r}\]= \[\dfrac{n!}{{(n-r)!}\ {r!}} \] which represents selecting r things randomly out of n things. Since it's two boys and one girl so there can be many possible outcomes. Find out that and then the probability of having two boys and one girl.
Complete step-by-step solution -
Given that the class has 15 boys and 5 girls. So the total no. of students = 20 and we have to select out only 3 members. So, the combination becomes \[{}^{20}{C_3}\]= \[\dfrac{{20 \times 19 \times 18}}{{3 \times 2}}\] = 1140
Three students are selected at random. To find the probability that there are two boys and one girl can be done as follow
Selection of two boys out of 15 can be done as \[{}^{15}{C_2}\] = \[\dfrac{15!}{{13!}\ {2!}}\] = \[\dfrac{{15 \times 14}}{2}\] = 105
Similarly, selection of one girl out of 5 can be done as \[{}^5{C_2}\] = \[\dfrac{5!}{{3!}\ {2!}}\] = \[\dfrac{5 \times 4}{2}\] = 10
Hence, the required probability is \[\dfrac{{{}^{15}{C_2} \times {}^5{C_1}}}{{1140}}\] = \[\dfrac{{105 \times 10}}{{1140}}\] = \[\dfrac{{35}}{{38}}\]
∴ the correct option is ‘A’
Note: Key concept of such types of problems is to find out all the favourable combinations which are possible. Here we use the multiplication method of probability as the selection of 3 members are dependent on each other.
Complete step-by-step solution -
Given that the class has 15 boys and 5 girls. So the total no. of students = 20 and we have to select out only 3 members. So, the combination becomes \[{}^{20}{C_3}\]= \[\dfrac{{20 \times 19 \times 18}}{{3 \times 2}}\] = 1140
Three students are selected at random. To find the probability that there are two boys and one girl can be done as follow
Selection of two boys out of 15 can be done as \[{}^{15}{C_2}\] = \[\dfrac{15!}{{13!}\ {2!}}\] = \[\dfrac{{15 \times 14}}{2}\] = 105
Similarly, selection of one girl out of 5 can be done as \[{}^5{C_2}\] = \[\dfrac{5!}{{3!}\ {2!}}\] = \[\dfrac{5 \times 4}{2}\] = 10
Hence, the required probability is \[\dfrac{{{}^{15}{C_2} \times {}^5{C_1}}}{{1140}}\] = \[\dfrac{{105 \times 10}}{{1140}}\] = \[\dfrac{{35}}{{38}}\]
∴ the correct option is ‘A’
Note: Key concept of such types of problems is to find out all the favourable combinations which are possible. Here we use the multiplication method of probability as the selection of 3 members are dependent on each other.
Recently Updated Pages
Basicity of sulphurous acid and sulphuric acid are
Assertion The resistivity of a semiconductor increases class 13 physics CBSE
The Equation xxx + 2 is Satisfied when x is Equal to Class 10 Maths
What is the stopping potential when the metal with class 12 physics JEE_Main
The momentum of a photon is 2 times 10 16gm cmsec Its class 12 physics JEE_Main
Using the following information to help you answer class 12 chemistry CBSE
Trending doubts
Difference Between Plant Cell and Animal Cell
Difference between Prokaryotic cell and Eukaryotic class 11 biology CBSE
Fill the blanks with the suitable prepositions 1 The class 9 english CBSE
Change the following sentences into negative and interrogative class 10 english CBSE
Summary of the poem Where the Mind is Without Fear class 8 english CBSE
Give 10 examples for herbs , shrubs , climbers , creepers
Write an application to the principal requesting five class 10 english CBSE
What organs are located on the left side of your body class 11 biology CBSE
What is the z value for a 90 95 and 99 percent confidence class 11 maths CBSE