Latest TCS Aptitude Question SOLUTION: 3. What is∑ ( ), where is the number of ways of choosing k items from 28 items? a. 406 * b. 306 * c. 28 * d. 56 *

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3. What is∑


(
), where

is the number of ways of choosing k items from 28
items?
a. 406 *


b. 306 *


c. 28 *


d. 56 *

Asked In TCS dinesh (10 years ago)

Unsolved Read Solution (3)

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kadali naga sindhuja  (10 years ago)

no of ways of choosing k items from 28= 28ck
therefore a=28ck
so k can be from minimum 1.
if k=1, 28c1=>28
if k=2, 28c2=>378
and so on.....
thus, starting from minimum 28only ,so (28*something) should be the result

Is this solution Helpfull? Yes (11) | No (2)  

utkarsh bisht  (10 years ago)

406*2^27 will be answer of it

Is this solution Helpfull? Yes (8) | No (6)  

Rincy juliet  (10 years ago)

Consider (1+x)n=C0+C1x+C2x2+…..+Cnxn …….(1)
Differentiating w.r.t x we get
n(1+x)n−1=C1+2C2x+3C3x2+…..+nCnxn−1
Multiplying by x on both sides,
x.n(1+x)n−1=x.C1+2C2x2+3C3x3+…..
Now again differentiating w.r.t to x
n(1+x)n−1+n(n−1)x(1+x)n−2=C0+22C1x+32C2x2+42C3x3…..
Putting x = 1, we get
n(n+1)2n−2=C1+22C2+32C3+42C4
Now substituting n = 28
28(28+1)228−2 = 812.226 = 406.227

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