Question

Find the sum of odd integers from 1 to 2001.

• A. 1001000
• B. 1000000
• C. 1002001
• D. 1003002

Answer 1

Answer:

C. 1002001

1,3,5,7,....,2001

$S_n=\frac{n}{2}[t_1+t_n]$

$a+(n-1)d=t_n$

$1+(n-1)2=2001$

$(n-1)2=2000$

n-1=1000

n=1001

$S_n=\frac{1001}{2}[1+2001]$

$=\frac{1001}{2}\times2002$

$=1001 \times1001$

$=1002001$