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

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