Question

1 supra 13 + 2 supra 13 + 3 supra 13 + ... + 51 supara 13 

Answer 1

             
$\frac{1}{13} + \frac{2}{13}+ \frac{3}{13}+... + \frac{51}{13}= \\ \\ = \frac{1}{13}(1+2+3+ ... +51)= \\ \\ = \frac{1}{13}* \frac{51(51+1)}{2} =\frac{1}{13}* \frac{51*52}{2}= \frac{51*52}{13*2}= \frac{51*52}{26}=51*2=\boxed{102}$