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Mohammed Fareed Ur Rahman from International Indian School , asked a question
Subject: Math , asked on 27/2/13

find the sum of all natural numbers between 250 and 1000 which are exacty divisible by 9

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Kanishk Ameta , From A. E. C. S. - 4 , added an answer
Answered on 28/2/13

a=252 (as it is next number divisible by 9)

d=9

l=999 (as last number divisible by 9)

to find n

999=252+(n-1)9

747=9n-9

756=9n

n=84

S84 =

84/2(252+999)= 52542

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Riya Arora , added an answer
Answered on 27/2/13

AP : 252 , 261 , - - - - - - - - - - - - - - - - - - -  - - -  999
a = 252 
d = 9
an = 999
an = a + (n-1) d 
999 = 252 + (n-1) 9
999 = 252 + 9n - 9
999 = 243 +9n
999-243 = 9n
756 = 9n
756/9 = n
n = 84

Sn = n/2 (a +an)
Sn = 84/2 (252 +999)
Sn = 24 (1251)
Sn = 30024