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1
JEE Main 2021 (Online) 27th July Evening Shift
MCQ (Single Correct Answer)
+4
-1
A student appeared in an examination consisting of 8 true-false type questions. The student guesses the answers with equal probability. the smallest value of n, so that the probability of guessing at least 'n' correct answers is less than $${1 \over 2}$$, is :
A
5
B
6
C
3
D
4
2
JEE Main 2021 (Online) 27th July Morning Shift
MCQ (Single Correct Answer)
+4
-1
The probability that a randomly selected 2-digit number belongs to the set {n $$\in$$ N : (2n $$-$$ 2) is a multiple of 3} is equal to
A
$${1 \over 6}$$
B
$${2 \over 3}$$
C
$${1 \over 2}$$
D
$${1 \over 3}$$
3
JEE Main 2021 (Online) 25th July Evening Shift
MCQ (Single Correct Answer)
+4
-1
Let X be a random variable such that the probability function of a distribution is given by $$P(X = 0) = {1 \over 2},P(X = j) = {1 \over {{3^j}}}(j = 1,2,3,...,\infty )$$. Then the mean of the distribution and P(X is positive and even) respectively are :
A
$${3 \over 8}$$ and $${1 \over 8}$$
B
$${3 \over 4}$$ and $${1 \over 8}$$
C
$${3 \over 4}$$ and $${1 \over 9}$$
D
$${3 \over 4}$$ and $${1 \over 16}$$
4
JEE Main 2021 (Online) 25th July Morning Shift
MCQ (Single Correct Answer)
+4
-1
Let 9 distinct balls be distributed among 4 boxes, B1, B2, B3 and B4. If the probability than B3 contains exactly 3 balls is $$k{\left( {{3 \over 4}} \right)^9}$$ then k lies in the set :
A
{x $$\in$$ R : |x $$-$$ 3| < 1}
B
{x $$\in$$ R : |x $$-$$ 2| $$\le$$ 1}
C
{x $$\in$$ R : |x $$-$$ 1| < 1}
D
{x $$\in$$ R : |x $$-$$ 5| $$\le$$ 1}
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