The sum of the first

Vipul
#1. May 13th, 2008, at 12:20 PM.

Answer is E.

Sum of first 100 integers = 5050
Sum of first 200 integers would be (5050 *2) +(100 * 100) = 20100

dennis
#2. May 13th, 2008, at 5:10 PM.

C

dennis
#3. May 13th, 2008, at 5:13 PM.

E

Asher
#4. May 13th, 2008, at 9:41 PM.

The question states the sum of the first 200 positive integers i.e. 1+2+3+4…200

this can be solved with the formula: n(n+1)/2 –> 200 (200+1)/2 = 20100.

Manisha
#5. May 14th, 2008, at 11:34 AM.

Can you please explain when do we use the above stated Formula……n(n+1)/2

Bhaskar
#6. May 14th, 2008, at 2:39 PM.

@Manisha

this is the general formula for sum of n integers n(n+1)/2. Please study Arithmetic Progression for more details.

Shivani
#7. May 15th, 2008, at 8:54 AM.

N(N+1)/2
= 200(200+1)/2
=20100
Ans E

Ritula
#8. May 15th, 2008, at 11:34 AM.

Sum of n integers is given by n(n+1)/2
Here n=200
therefore, sum of 200 integeres =200(200+1)/2=20100
So correct answer is E

Manisha
#9. May 15th, 2008, at 12:26 PM.

@ Thanku Bhaskar for telling me the usage of formula stated above.

Becoz its related to above question, i just wanted to know, if we have to find out the sum of integers from 101 to 200, do we have any formula for the same…….?
Since n(n+1)/2 can’t be used in such a case……

Amar
#10. May 15th, 2008, at 2:18 PM.

Answer E
using n(n+1)/2

Rajib Banerjee
#11. May 15th, 2008, at 9:02 PM.

Actually, the base formula is
S = n[2a + (n-1)d]/2
where n = number of terms, S = sum of terms, a = first term(=1)
and d = difference between the terms ( =1 )
so, our question is
1+2+3+4…………………+200
Just and FYI 200(l) is the last term term, so it can be calculated as,
l = a + (n-1)d

Kamal Patel
#12. May 15th, 2008, at 9:48 PM.

This can be look at like:
1 + 199 = 200
2 + 198 = 200
3 + 197 = 200
…
so there are 99 of those plus 1 more for the 200 value. We also have 1 100 value in the middle left so:
(200 * 100) + 100 = 20000 + 100 = 20100 (E)

Neema
#13. May 18th, 2008, at 10:26 AM.

Wow!!! Kamal that was a wonderful logic!!

rupa
#14. May 20th, 2008, at 10:48 AM.

c-is the correct answer

kartik
#15. May 21st, 2008, at 10:32 AM.

Ans : e
another logic :
5050 + (101+102+103….200)
5050 + ((100 +1)+(100+2) +100+3)…(100+100))
taking the 100 to 1 group and the rest to the other
5050 + ((100*100) + (1+2+3….100))
we no the 2nd group = 5050 and 100* 100 = 10000
5050 + (10000 + 5050) = 20100
thanks