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Numbers - General Aptitude

Q1:

1 - 1 + 1 - 2 + 1 - 3 + ... up to n terms = ?
n n n

A
1 n
2

B
1 (n - 1)
2

C
1 n(n - 1)
2

D None of these

ANS:B -

1 (n - 1)
2

Given sum
= (1 + 1 + 1 + ... to n terms) - 1 + 2 + 3 + ... to n terms
n n n
 
= n - n 1 + 1     [ Ref: nth terms = (n/n) = 1]
2 n
 
= n - n + 1
2
 
= 1 (n - 1)
2