Find the sum of all integers wich are divisible by 7 and lying between 50 and 500.

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Numbers between 50 and 500

The first number dividible by 7 is 56 , then 56+7 , ......500

56, (56+7) 56+ (2*7) + (56+3*7) + .....+ (56 + 63*7)

Then the sum:

Sn = (n/2)*(an+a1)

     = 64/2 (497+ 56)

     = 32* 553

     = 17,696

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