1
WB JEE 2020
+1
-0.25
Four persons A, B, C and D throw an unbiased die, turn by turn, in succession till one gets an even number and win the game. What is the probability that A wins if A begins?
A
$${1 \over 4}$$
B
$${1 \over 2}$$
C
$${7 \over 12}$$
D
$${8 \over 15}$$
2
WB JEE 2020
+1
-0.25
A rifleman is firing at a distant target and has only 10% chance of hitting it. The least number of rounds he must fire to have more than 50% chance of hitting it at least once, is
A
5
B
7
C
9
D
11
3
WB JEE 2019
+1
-0.25
A problem in mathematics is given to 4 students whose chances of solving individually are $${{1 \over 2}}$$, $${{1 \over 3}}$$, $${{1 \over 4}}$$ and $${{1 \over 5}}$$. The probability that the problem will be solved at least by one student is
A
$${{2 \over 3}}$$
B
$${{3 \over 5}}$$
C
$${{4 \over 5}}$$
D
$${{3 \over 4}}$$
4
WB JEE 2019
+1
-0.25
If X is a random variable such that $$\sigma$$(X) = 2.6, then $$\sigma$$(1 $$-$$ 4X) is equal to
A
7.8
B
$$-$$ 10.4
C
13
D
10.4
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