The numbers in the last row are $ 50, $ $ 49, $ $ 48, $ $ 47, $ $ 46, $ so we want to find the sum \[5+6+15+16+\dots+45+46.\] The sum of an arithmetic series is equal to the average of the first and last term, multiplied by the number of terms. We first add $ 5+15+25+35+45 $ by observing that the mean of these five terms is $ 25, $ so their sum is $ 25\cdot5 $. Similarly, the mean of the five terms in the sum $ 6+16+26+36+46 $ is $ 26, $ so their sum is $ 26\cdot 5 $. Adding these sums, we find that the original sum is $$25\cdot5+26\cdot 5=(25+26)\cdot5=51\cdot5=\boxed{255}.$$