Question

find the sum of all three digit number which leave the same remindrer 2 which divided by 5

Answer 1

102, 107, 112..............................997

a = 102, last term (an) = 997,  d = 5

an   = a+ (n-1)d
997 =102 + (n-1)*5

997-102 = (n-1)*5

895/5 = n-1
179 = n-1
n = 180

Sn = n/2 (a+l)1
     = 180/2 (102 +997)
     = 90*1099
     =98910

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