a die is thrown twice what is the probability that 1. 5 will not come up either time. 2 . 5 will come up at least once
Answers
Answer:
1. 25/36
2. 11/36
Step-by-step explanation:
1. possible outcomes =
1,1
1,2
1,3
1,4
1,5
1,6
2,1
2,2
2,3
2,4
2,5
2,6
3,1
3,2
3,3
3,4
3,5
3,6
4,1
4,2
4,3
4,4
4,5
4,6
5,1
5,2
5,3
5,4
5,6
6,1
6,2
6,3
6,4
6,5
6,6
total no. of outcomes = 36
total no. of times that 5 will not come up either time = 36-11 = 25
probability = 25/36
2. total no. of outcomes = 36
total no. of times that 5 will come up at least once = 11
probability = 11/36
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Outcomes are:
(1, 1), (1, 2), (1, 3), (1, 4), (1, 5), (1, 6)
(2, 1), (2, 2), (2, 3), (2, 4), (2, 5), (2, 6)
(3, 1), (3, 2), (3, 3), (3, 4), (3, 5), (3, 6)
(4, 1), (4, 2), (4, 3), (4, 4), (4, 5), (4, 6)
(5, 1), (5, 2), (5, 3), (5, 4), (5, 5), (5, 6)
(6, 1), (6, 2), (6, 3), (6, 4), (6, 5), (6, 6)
So, the total number of outcome = 6 × 6 = 36
Method 1:
Consider the following events.
A = 5 comes in the first throw,
B = 5 comes in second throw
P(A) = 6/36,
P(B) = 6/36 and
P(not B) = 5/6
So, P(notA) = 1 – 6/36 = 5/6
∴ The required probability = 5/6 × 5/6 = 25/36
Method 2:
Let E be the event in which 5 does not come up either time.
So, the favourable outcomes are [36 – (5 + 6)] = 25
∴ P(E) = 25/36
• Number of events when 5 comes at least once = 11 (5 + 6)
∴ The required probability = 11/36