Answer: B 2 balls can be drawn in the following ways 1 red, 1 green or 2 red or 2 green Required probability =(2C1*3C1)/7C2 + 2C2/7C2 + 3C2/ 7C2 => 6/21 + 1/21 + 3/21 = 10/21
Q. No. 8:
I forgot the last digit of a 7-digit telephone number. If 1 randomly dial the final 3 digits after correctly dialing the first four, then what is the chance of dialing the correct number?
Answer: B It is given that last three digits are randomly dialled. then each of the digit can be selected out of 10 digits in 10 ways. Hence required probability = (1/10)3= 1/1000
Q. No. 9:
In his wardrobe, Dishant has three trousers. One of them is black the second is blue, and the third brown. In his wardrobe, he also has four shirts. One of them is black and the other 3 are white. He opens his wardrobe in the dark and picks out one shirt and one trouser pair without examining the colour. What is the likelihood that neither the shirt nor the trouser is black?
Answer: D Probability that trouser is not black =2/3 probability that shirt is not black = 3/4 Required probability = 2/3 * 3/4 = 1/2
Q. No. 10:
Abhishek has 9 pairs of dark blue socks and 9 pairs of black socks. He keeps them all in the same bag. If he picks out three socks at random, then what is the probability that he will get a matching pair?
Answer: A There are total 5 letters. The probability that B gets the first position is 1/5. The probability that G is in the second position is 1/4. Likewise, probability for I,N and G = 1/3,1/2 and 1/1 respectively. Hence required probability = 1/5 * 1/4 * 1/3 * 1/2 * 1/1 = 1/120
Q. No. 12:
Four boys and three girls stand in queue for an interview. The probability that they stand in alternate positions is
Answer: A Total number of possible arrangements for 4 boys and 3 girls in a queue = 7! when they occupy alternate position the arrangement would be like B G B G B G B Thus, total number of possible arrangements for boys = (4*3*2) Total number of possible arrangements for girls =(3*2) required probability = (4*3*2*3*2)/7! = 1/35.