Brain-Teaser 882: Another magic class

From The Sunday Times, 2nd July 1978 [link]

This puzzle concerns a class of twenty-five pupils whose first names happen to have different initials (and none begins with X). The teacher makes them sit in alphabetical order in five neat rows of five with Arthur sitting to the left of Barry and in front of Freda.

When their homework was returned (marked, as usual, out of a maximum of 25 without using fractional marks) they found that each pupil had a different mark and that, surprisingly enough, the total of marks in each row of five, each column of five and each diagonal of five was identical.

Yvonne came top, followed by Harry and Jane in that order. Ursula scored more marks than Zena, and Richard was beaten by Charles. Victor had twice as many marks as George, and Ivor had four times as many as Freda. Susan beat Michael by the same margin by which Michael beat George (who, incidentally, scored an odd number of marks). This was also the margin by which Walter beat his left-hand neighbour and by which his right-hand neighbour beat him.

Kenneth beat Olga. By how many marks?

This puzzle is included in the book The Sunday Times Book of Brain-Teasers: Book 1 (1980). The puzzle text above is taken from the book.

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