The average of the $N$ integers
\[ N+1, N+2, N+3, \ldots 2N \]
is 80. What is N?
Using the formula (a+b)/2*n
we have $a$ as the first term
and $b$ as the last term
$(3N+1)/2*N=80*N$
Since it is average we have to multiply by the amount of terms
Solving we get $N=53$
