elitmus
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Numerical Ability
Number System
if n greater than 100 and sum of 101+102+------+n, what is the the probability that the sum will be divisible by (n-100)
a) 3/4
b) 1/3
c) 1/2
d) None of above
Read Solution (Total 6)
-
- c) 1/2
S = 101+102+------+n
S = (1+2+...+101+102+...+n)-(1+2+...+100)
S = n(n+1)/2 - 100*101/2
S = 1/2 *(n^2+n-100*101)
S = 1/2 *(n+101)(n-100)
if n is even, S is not divisible by (n-100)
if n is odd, S is divisible by (n-100)
so, probability is = 1/2 - 10 years agoHelpfull: Yes(73) No(7)
- @rakesh- when sum has a factor of (n-100) in it, that itself means it is completely divisible by (n-100).
So, don't you think it is completely divisible, independent of value of n, so probability is 1. - 10 years agoHelpfull: Yes(17) No(9)
- a=101,d=1;
Sn = n/2(2*101+n-1)
Sn= (n^2+201n)/2
let chk Sn divisible by (n-100)
(n^2+201n)/2(n-100)
depend n is even or odd but Denominator is even.
if n is even--- even/even
else n is odd ---- odd/even
so C)1/2 may be right ans....
- 10 years agoHelpfull: Yes(6) No(2)
- @trisha 1/2*(n+101).....this must be a integer for sum to have
n-100 as factor so for 1/2*(n+101) being an integer n+101 must be a even no. so
probability is 1/2 - 10 years agoHelpfull: Yes(2) No(0)
- sum=[n-101+1][101+n]/2
=(n-100)(101+n)/2
prob={(n-100)(101+n)/2}/n-100
so,ans is=D - 10 years agoHelpfull: Yes(1) No(5)
- @trisha .. probablity cant be 1
bcozz take example of 106 . dis doesn't agree the term - 10 years agoHelpfull: Yes(0) No(0)
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