Find the sum of all multiples of 7 lying between 500 and 900

1.	Find the sum of all multiples of 7 lying between 500 and 900
Answer» 39900 sum 504 , 511 , 518 , ....,889, 896 are multiples of 7 between 500 and 900 and these are in Arithmetic progression .First term = a = 504 , Common difference = a2 - a1 = d = 511 - 504 = 7Let the number of terms = nLast term ( L ) = 896We know that ,a + ( n - 1 )d = L504 + ( n - 1 ) 7 = 896Divide each term with 7 , we get72 + n - 1 = 12871 + n = 128n = 128 - 71n = 57\xa0 Calculate?

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