sbi po question

Question

In a bag there are three types of colored balls of red, white and Bluecolors. The probability of selecting one red ball out of the total ball is 1/2 and the probability of selecting one blue ball out of the total ball is 2/7.The number of
white balls in the bag is 6.
1. If all the ball are numbered starting from 1, 2, 3, …………….and so on then what is the probability of selecting one ball
which is numbered as a multiple of 3 or 7 out of the total balls.
(a) 3
7
(b) 5
14
(c) 1
12
(d) 6
11
(e) none of these
2. What are the total number of balls in the bag?
(a)28 (b)30 (c)35
(d)40 (e)none of these

Answer 1

We know that P(red) = 1/2 and P(blue) = 2/7

Restating these probabilities with common denominators we have

P(red) = 7/14 and P(blue) = 4/14

P(red or blue) = 11/14 so P(white)=3/14

 

Since there are 6 white balls, there must be a total of 28 balls including

14 red

8 blue

6 white

 

1.

With 28 numbered balls, the balls that are multiples of 3 are

3 6 9 12 15 18 21 24 27 for a total of 9 balls

Those that are multiples of 7 are

7 14 21 28 for a total of 4 balls

But notice, one ball, #21, appears in both lists

So the P(of selecting a ball that is a multiple of 3 or 7) = (9+4-1)/28 = 12/28 = 3/7 (A)

 

2.

already answered above.  There are 28 balls in the bag.  (A)