NARAYANA IIT ACADEMY JEE MAIN – 2013 - Narayana Group

(3) x 2 + y 2 – 6y – 5 = 0 (4) x -2 + y 2 – 6y + 5 = 0
Ans. (1)
Sol. Foci of the ellipse are
7,0
radius of the circle = 4
equation of circle is
x 2 + y 2 – 6y – 7 = 0.
78. A multiple choice examination has 5 questions. Each question has three alternative answers
of which exactly one is correct. The probability that a student will get 4 or more correct
answers just by guessing is :
17
13
11
(1) (2) (3)
5
5
5
3
3
3
Ans. (3)
Sol. Required probability = P (4 correct answer by guessing)
+ P (5 correct answer by guessing)
4 5
10
(4)
5
3
1 2 1
= 5
C
. . 5
4
C5
3 3 3
11
=
5
3 .
79. The x-coordinate of the incentre of the triangle that has the coordinates of mid points of its
sides as (0, 1), (1, 1) and (1, 0) is
(1) 2 2
(2) 2 2
(3) 1 2 (4) 1
2
Ans. (2)
x coordinate of incentre
0 4 0 4
=
2
2 2 2 2 4 2 2
2
C(0, 2)
2Ö2
2
(0, 1)
(1, 1)
A(0, 0) (1, 0) B(2, 0)
2
80.
x 1 x 1
The term independent of x in the expansion of
2/3 1/3 1/2
x x 1 x x
is
(1) 4 (2) 120 (3) 210 (4) 310
Ans. (3)
NARAYANA IIT ACADEMY JEE MAIN – 2013
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