Question

A jar contained 8 balls: 6 red, 1 green and 1 blue. We randomly take a ball out of the jar. Once a ball is selected we do not put it back. We keep selecting balls until for the first time we get a blue one. We count the number of times we had to draw a ball, (including the last drawing) until we actually got the blue ball. How many elements are in the sample space for this experiment

Answer 1

35

Explanation:

Given that :

Number of balls = 8

Red (R) = 6 ; 1 green(G) ; 1 BLUE (B)

Possibilities unt a blue ball is picked :

B, RB, GB, RRB, RGB, GRB, G

Draw 1 = B = 1

Draw 2 = B = 2C1 = 2

Draw 3 = B = 3C2 = 3

Draw 4 = B = 3C3 + 3C1 = 1 + 3 = 4

Draw 5 = B = 4C4 + 4C1 = 1 + 4 = 5

Draw 6 = B = 5C5 + 5C1 = 1 + 5 = 6

Draw 7 = B = 6C6 + 6C1 = 1 + 6 = 7

Draw 8 = B = 6C6 + 6C1 = 1 + 6 = 7

Taking the sum:

(1 + 2 + 3 + 4 + 5 + 6 + 7 + 7) = 35

There are 35 elements in the sample space