Percentage is different when convert Total Number from 75 or 50 to 100

Question

I am creating Student result sheet facing a problem when I Convert Total Marks from 75 or 50 to 100 I get difference in percentage

on left side where total is 75 or 50 its 37.55% and on right where total is 100 its 36.67%

+-------+-------+----------+---------+--+-------+-------------+---------+
| Total | Marks | Obtained | Percent |  | Marks |  Obtained   | Percent |
+-------+-------+----------+---------+--+-------+-------------+---------+
|       |    75 |       40 | 53.33%  |  |   100 | 53.33333333 | 53.33%  |
|       |    75 |       13 | 17.33%  |  |   100 | 17.33333333 | 17.33%  |
|       |    75 |       25 | 33.33%  |  |   100 | 33.33333333 | 33.33%  |
|       |    75 |       38 | 50.67%  |  |   100 | 50.66666667 | 50.67%  |
|       |    75 |     30.5 | 40.67%  |  |   100 | 40.66666667 | 40.67%  |
|       |    75 |       33 | 44.00%  |  |   100 |          44 | 44.00%  |
|       |    50 |     15.5 | 31.00%  |  |   100 |          31 | 31.00%  |
|       |    50 |     11.5 | 23.00%  |  |   100 |          23 | 23.00%  |
|       |       |          |         |  |       |             |         |
| Total |   550 |    206.5 | 37.55%  |  |   800 | 293.3333333 | 36.67%  |
+-------+-------+----------+---------+--+-------+-------------+---------+

Percentage Difference

Answer 1

It is not surprising. When you scale everything up to $100$ you are weighting the two lines with $50$ marks possible more heavily than they were in the first total. Since they were below average efforts the percentage goes down. If the last exam had had $5,000,000$ marks available and the student had gotten $1,150,000$ that would dominate the left column and the average there would be (very close to) $23\%$. Somebody needs to decide how the exams should be weighted.