A) 15
B) 14
C) 12
D) 7
Correct Answer: B
Solution :
Probability that head occurs 6 times \[={}^{n}{{C}_{6}}{{\left( \frac{1}{2} \right)}^{6}}{{\left( \frac{1}{2} \right)}^{n-6}}\] and probability that head occurs 8 times \[={}^{n}{{C}_{8}}{{\left( \frac{1}{2} \right)}^{8}}{{\left( \frac{1}{2} \right)}^{n-8}}\] \[\therefore \,\,\,{}^{n}{{C}_{6}}{{\left( \frac{1}{2} \right)}^{6}}{{\left( \frac{1}{2} \right)}^{n-6}}={}^{n}{{C}_{8}}{{\left( \frac{1}{2} \right)}^{8}}{{\left( \frac{1}{2} \right)}^{n-8}}\] \[{}^{n}{{C}_{6}}={}^{n}{{C}_{8}}\] Þ \[(n-6)(n-7)=56\Rightarrow n=14\].
You need to login to perform this action.
You will be redirected in
3 sec
