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The probability that 9 students pass in Mathematics, Physics and Chemistry are m, p and c respectively, of these subject the students has a 75% chance of passing in at least one subject 50% chance of passing in at least two subject and 40% chance of passing in exactly two. Which of the following relation are true ?
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- p + m + c =19/20
- p + m + c = 17/20
- pmc = 1/10
- pmc = 1/4
Correct Option: C
P(M) = m, P (p) = p, P(c) = c
∵ The probability of at least one success
= P (M ∪ P ∪ C)
= m + p + c -mp - mc - pc + mcp = 3/4 ...(1)
The probability of at least two successes = mcp + mcp + mcp + mcp
= mc(1 - p) + mp (1 - c ) + (1 - m )cp + mcp
= mc + mp + cp - 2mcp = 1/2
The probability of exactly two success
= mcp + mcp + mcp
= mc(1 - p) + mp (1 - c ) cp(1 - m )
= mc + mp + cp - 3 mcp = 2/5
(2) & (3) gives,
⇒ mcp = 1/2 - 2/5 = 1/10
∴ mc + mp + cp = 2/10 + 1/2 = 1/5 + 1/2 = 7/10
From (1),
m + p + c - 7/10 + 1/10 = 3/4
⇒ m + p + c = 3/4 + 7/10 - 1/10 = 27/20
Thus, pmc = 1/10 is a true relation.
