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Binomial Theorem · Question 22

JEE Main 2025 (Online) 7th April Evening ShiftNumericalHard📈 Topic in 52% papers+4
1

The sum of the series 2 1 20C4 - 3 2 20C5 + 4 3 20C6 - 5 4 20C7 + + 18 17 20C20, is equal to .

Answer

34

Solution

The general term (r = 4 to 20) is (-1)r (r - 2)(r - 3) 20Cr.

(r = 4 gives +2 1 20C4, r = 20 gives +18 17 20C20.)

Since (r - 2)(r - 3) is a polynomial in r of degree 2 (< 20),

r=020 (-1)r (r - 2)(r - 3) 20Cr = 0

(because (-1)r nCr = (-1)r r nCr = (-1)r r(r - 1) nCr = 0 for n = 20)

S = - r=03 (-1)r (r - 2)(r - 3) 20Cr

r = 0: (+1)(-2)(-3)(1) = 6

r = 1: (-1)(-1)(-2)(20) = -40

r = 2, 3: the factor (r - 2)(r - 3) = 0

S = -(6 - 40) = 34

Answer: 34

JEE Main 2025 (Online) 7th April Evening Shift

Keep practising — Binomial Theorem

2

For an integer n 2, if the arithmetic mean of all coefficients in the binomial expansion of (x + y)2n - 3 is 16, then the distance of the point P (2n - 1, n2 - 4n ) from the line x + y = 8 is

  1. 2
  2. 2 2
  3. 5 2
  4. 3 2
JEE Main 2025 (Online) 4th April Morning Shift
3

In the expansion of ( [3]2 + 1 [3]3 )n, n N, if the ratio of 15th term from the beginning to the 15th term from the end is 16, then the value of nC3 is

  1. 4960
  2. 2300
  3. 1040
  4. 4060
JEE Main 2025 (Online) 4th April Morning Shift
4

If 12 (15C1 ) + 22 (15C2 ) + 32 (15C3 ) + + 152 (15C15 ) = 2m 3n 5k, where m, n, k N, then m + n + k is equal to :

  1. 20
  2. 19
  3. 18
  4. 21
JEE Main 2025 (Online) 4th April Evening Shift
5

The sum of all rational terms in the expansion of (2+ 3)8 is :

  1. 16923
  2. 18817
  3. 3763
  4. 33845
JEE Main 2025 (Online) 3rd April Morning Shift
6

If r=19 ( r+32r ) 9Cr = ( 32 )9 - , , N, then ( + )2 is equal to

  1. 27
  2. 81
  3. 18
  4. 9
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7

Let (1 + x + x2 )10 = a0 + a1x + a2x2 + + a20x20. If (a1 + a3 + a5 + + a19) - 11a2 = 121k, then k is equal to .

JEE Main 2025 (Online) 3rd April Evening Shift
8

The term independent of x in the expansion of ( (x + 1)(x2/3 + 1 - x1/3) - (x - 1)(x - x1/2) )10, x > 1, is :

  1. 240
  2. 120
  3. 150
  4. 210
JEE Main 2025 (Online) 2nd April Morning Shift
9

If r=010 ( 10r+1 - 110r ) 11Cr+1 = 11 - 11111010, then is equal to :

  1. 11
  2. 20
  3. 24
  4. 15
JEE Main 2025 (Online) 2nd April Evening Shift
10

The least value of n for which the number of integral terms in the Binomial expansion of ( [3]7 + [12]11)n is 183, is :

  1. 2184
  2. 2172
  3. 2196
  4. 2148
JEE Main 2025 (Online) 29th January Morning Shift
11

If = 1 + r=16(-3)r-1 12C2r-1, then the distance of the point (12, 3) from the line x - 3y + 1 = 0 is .

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