Question 33250
1. The probability of picking a multiple of 5 from cards num 1 to 20:
There are 4 cards from card number 1 to 20 that are multiple of 5; 
So, the probability of picking a number which is a multiple of 5 is 4/20 = .2; 
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2. a bag has 2 red 7 yellow, 4 blue what are the prob.of getting a.picking a blue marble ,not picking a yellow, getting 2 blue. 
The question does not state the number of marbles to be drawn at a time.  It is assumed one marble is picked at a time.
Total number of balls = 13;
Total number of blue marbles = 4;
Number of marbles other than yellow = 6;
a. Probability of picking a blue marble = 4/13;
b. Probability of picking a marble other than yellow = 6/13;
c. Probability of picking 2 blue marbles (one at a time)
= [4/13]*[3/12] = 1/13;
3.when rollong two num. cubes what is the probability of getting sum of 4 
Total number of combinations = 36 (6*6);
Total number of combinations to have a sum of 4 = 3 (1,3; 3,1; 2,2)
Probability of getting sum of 4 = 3/36 = 1/12;