Permutation And Combination Ques 5
Question-
In a group of 6 boys and 4 girls, four children are to be selected. In how many different ways can they be selected such that at least one boy should be there?
(1) 159
(2) 194
(3) 205
(4) 209
(5) None of these
(Bank of Baroda PO Exam, 25.09.2016) (SBI Banks PO Exam. 20.08.2000)
Show Answer
Correct Answer: (4)
Solution: (4)
Ways of selections $\Rightarrow$ (1 boy and 3 girls) or ( 2 boys and 2 girls) or ( 3 boys and 1 girl) or 4 boys.
$\therefore$ Required number of ways $=\left({ }^{6} C_{1} \times{ }^{4} C_{3}\right)+\left({ }^{6} C_{2} \times{ }^{4} C_{2}\right)+\left({ }^{6} C_{3}\right.$ $\left.\times{ }^{4} C_{1}\right)+{ }^{6} C_{4}$ $=\left({ }^{6} C_{1} \times{ }^{4} C_{1}\right)+\left({ }^{6} C_{2} \times{ }^{4} C_{2}\right)+\left({ }^{6} C_{3}\right.$
$\left.\times{ }^{4} C_{1}\right)+{ }^{6} C_{2}$ $=(6 \times 4)+\left(\frac{6 \times 5}{2 \times 1} \times \frac{4 \times 3}{2 \times 1}\right)+$
$\left(\frac{6 \times 5 \times 4}{3 \times 2 \times 1} \times 4\right)+\left(\frac{6 \times 5}{2 \times 1}\right)$ $=24+90+80+15=209$