The sum of one set of 7 consecutive no's : 
1 + 2  + 3 + 4 + 5 + 6 + 7 = 28

The sum of another set of 7 consecutive numbers :
3 + 4 + 5 + 6 + 7 + 8 + 9 = 42

Which of the these no's could be the sum of yet another set of 7 consecutive no's?

a) 34
b) 63
c) 68
d) 73

Let the first no be n so the other numbers are n+1,n+2,n+3,n+4,n+5,n+6
Sum = 7n+21 =7(n+3) = 7k means divisible by 7.
So option b, 63

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