A six faced fair dice is thrown until 1 comes, then the probability th...
In single throw of a dice, probability of getting 1 is =
and prob. of not getting 1 is
Then getting 1 in even no. of chances = getting 1 in 2nd chance or in 4th chance or in 6th chance and so on
∴ Req. Prob
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A six faced fair dice is thrown until 1 comes, then the probability th...
Solution:
Let's consider the possible outcomes of the first few throws of the dice:
- If 1 comes in the first throw itself, it will be an even number of trials.
- If 1 comes in the second throw, it will be an odd number of trials.
- If 1 comes in the third throw, it will be an even number of trials.
- If 1 comes in the fourth throw, it will be an odd number of trials.
- If 1 comes in the fifth throw, it will be an even number of trials.
- If 1 comes in the sixth throw, it will be an odd number of trials.
- and so on...
So, we can see that the probability of getting 1 in an even number of throws is the sum of probabilities of getting 1 in the first, third, fifth, seventh, etc. throws.
Let's denote the probability of getting 1 in the first throw as p, and the probability of not getting 1 in the first throw as q. Since the dice is fair, we have:
p = 1/6 and q = 5/6
The probability of getting 1 in the third throw is the probability of not getting 1 in the first two throws (which is q*q) multiplied by the probability of getting 1 in the third throw (which is p):
P(1 on third throw) = q*q*p = (5/6)*(5/6)*(1/6)
Similarly, the probability of getting 1 in the fifth throw is:
P(1 on fifth throw) = q*q*q*q*p = (5/6)*(5/6)*(5/6)*(5/6)*(1/6)
And so on...
So, the probability of getting 1 in an even number of throws is:
P(1 in even number of trials) = P(1 on first throw) + P(1 on third throw) + P(1 on fifth throw) + ...
= p + (q*q*p) + (q*q*q*q*p) + ...
= p * (1 + q*q + q^4 + ...)
= p * (1/(1-q^2))
= (1/6) * (1/(1-(5/6)^2))
= 5/11
Therefore, the correct answer is option A) 5/11.
A six faced fair dice is thrown until 1 comes, then the probability th...