1
JEE Main 2018 (Offline)
MCQ (Single Correct Answer)
+4
-1
Change Language
If $$\sum\limits_{i = 1}^9 {\left( {{x_i} - 5} \right)} = 9$$ and

$$\sum\limits_{i = 1}^9 {{{\left( {{x_i} - 5} \right)}^2}} = 45$$, then the standard deviation of the 9 items
$${x_1},{x_2},.......,{x_9}$$ is
A
3
B
9
C
4
D
2
2
JEE Main 2018 (Offline)
MCQ (Single Correct Answer)
+4
-1
Change Language
A bag contains 4 red and 6 black balls. A ball is drawn at random from the bag, its colour is observed and this ball along with two additional balls of the same colour are returned to the bag. If now a ball is drawn at random from the bag, then the probability that this drawn ball is red, is :
A
$${3 \over 4}$$
B
$${3 \over 10}$$
C
$${2 \over 5}$$
D
$${1 \over 5}$$
3
JEE Main 2018 (Offline)
MCQ (Single Correct Answer)
+4
-1
Out of Syllabus
Change Language
If sum of all the solutions of the equation

$$8\cos x.\left( {\cos \left( {{\pi \over 6} + x} \right).\cos \left( {{\pi \over 6} - x} \right) - {1 \over 2}} \right) = 1$$

in [0, $$\pi $$] is k$$\pi $$, then k is equal to
A
$${{20} \over 9}$$
B
$${2 \over 3}$$
C
$${{13} \over 9}$$
D
$${{8} \over 9}$$
4
JEE Main 2018 (Offline)
MCQ (Single Correct Answer)
+4
-1
Out of Syllabus
Change Language
PQR is a triangular park with PQ = PR = 200 m. A T.V. tower stands at the mid-point of QR. If the angles of elevation of the top of the tower at P, Q and R are respectively 45$$^\circ $$, 30$$^\circ $$ and 30$$^\circ $$, then the height of the tower (in m) is :
A
$$50\sqrt 2 $$
B
100
C
50
D
$$100\sqrt 3 $$
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