Question
In how many ways can Rs. 16 be divided into 4 person when none of them get less than Rs. 3
Answer: Option B
:
B
Required number of ways
= coefficient of x16 in (x3+x4+x5+.......x7)4
= coefficient of x16 in x12(1+x+x2+.......x4)4
= coefficient of x16 in x12(1−x5)4(1−x)−4
= coefficient of x4 in (1−x5)4(1−x)−4
= coefficient of x4 in (1−4x5+.....)
[1+4x+....+(r+1)(r+2)(r+3)3!x]
= (4+1)(4+2)(4+3)3! = 35
Aliter: Remaining 4 rupees can be distributed in 4+4−1C4−1 i.e., 35 ways
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:
B
Required number of ways
= coefficient of x16 in (x3+x4+x5+.......x7)4
= coefficient of x16 in x12(1+x+x2+.......x4)4
= coefficient of x16 in x12(1−x5)4(1−x)−4
= coefficient of x4 in (1−x5)4(1−x)−4
= coefficient of x4 in (1−4x5+.....)
[1+4x+....+(r+1)(r+2)(r+3)3!x]
= (4+1)(4+2)(4+3)3! = 35
Aliter: Remaining 4 rupees can be distributed in 4+4−1C4−1 i.e., 35 ways
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