Question

A fair dice is thrown 20 Times. The probability that on the tenth throw the fourth six appear is _______

(a) [{(²⁰ ₁₀) ∙ 5⁶}/6²⁰]

(b) [(120 × 5⁷)/6¹⁰]

(c) [(84 × 5⁶)/6¹⁰] 

(d) None

Answer 1

The correct option (c) [(84 × 5⁶)/6¹⁰]   

Explanation:

given: dice thrown 20 times. ON 10^th throw, 4^th six should appear i.e. in first 9 throws, 3 sixes and 6 non sixes and six on 10^th throw so that it will be 4^th six irrespective of what face then after.

∴ P(event) = (⁹C₃)(1/6)³ (5/6)⁶ (1/6) = 84 × (5⁶ / 6¹⁰).