Find the sum of all intrgers between 50 and 500 ,which are divisible of 7
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The arithmetic series is 56+63+70+77+....+448
a=56 ,d=7 ,l=448
Number of terms n=l-a/d+1
n=448-56/7+1
=392/7+1
=56+1
=57
Sn=n/2(a+l)
S =57/2(56+448)
57
=57/2(504)
=57(252)
=14364
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