Question

Q(3)It is known that only 60% of a defected computer can be   

   repaired. A sample of 15 computers is selected randomly,   

   find the probability that;

 (i) None can be repaired  ​        

 (ii) 5 or less can be repaired ​     

(iii) At least 3 computers can be repaired. 

 

Answer 1

Laptop, which can be repaired $=60\%$

Total number of computer = 15

Total number of laptop which can be repaired $= 60\times \frac{15}{100} =9$

Total number of laptop which can not be repaired $= 6$

a) Probability, to find the laptop which can not be prepared $=\frac{6}{15}=\frac{2}{5}$

b) The required probability $=\frac{C^9_5}{C^{16}_5}=\frac{9\times 8\times 7\times 6}{16\times15\times14\times 13}$

$=\frac{9}{130}$

c) The required probability $=\frac{C^9_3}{C^{16}_3}=\frac{9\times 8\times 7}{16\times 15\times 14}$

$=\frac{3}{20}$