1
WB JEE 2008
MCQ (Single Correct Answer)
+1
-0.25

If the magnitude of the coefficient of x7 in the expansion of $${\left( {a{x^2} + {1 \over {bx}}} \right)^8}$$, where a, b are positive numbers, is equal to the magnitude of the coefficient of x7 in the expansion of $${\left( {ax + {1 \over {b{x^2}}}} \right)^8}$$, then a and b are connected by the relation

A
ab = 1
B
ab = 2
C
a2b = 1
D
ab2 = 2
2
WB JEE 2008
MCQ (Single Correct Answer)
+1
-0.25

If $${}^{16}{C_r} = {}^{16}{C_{r + 1}}$$, then the value of $${}^r{P_{r - 3}}$$ is

A
31
B
120
C
210
D
840
3
WB JEE 2008
MCQ (Single Correct Answer)
+1
-0.25

The coefficient of x$$-$$10 in $${\left( {{x^2} - {1 \over {{x^3}}}} \right)^{10}}$$ is

A
$$-$$ 252
B
$$-$$ 210
C
$$-$$ (5!)
D
$$-$$ 120
4
WB JEE 2009
MCQ (Single Correct Answer)
+1
-0.25

If C0, C1, C2, ......, Cn denote the coefficients in the expansion of (1 + x)n then the value of C1 + 2C2 + 3C3 + ..... + nCn is

A
n . 2n $$-$$ 1
B
(n + 1)2n $$-$$ 1
C
(n + 1)2n
D
(n + 2)2n $$-$$ 1
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