The big pile of apples contains the same amount
of large apples of a quarter of a euro each (from mrs. Jones), as smaller
apples of one sixth euro each (from mrs. Smith). The average price
is therefore (1/4 + 1/6) / 2 =
5/24 euro. But the apples are sold for
1/5 euro each (5 apples for 1 euro).
This means that per sold apple there is a
shortage of 5/24 - 1/5 = 1/120 euro.
The total shortage is 3.50 euro, so the ladies together started
out with 420 apples. These are worth 1/5
× 420 = 84 euro, or with equal division 42 euro for
each. If Mrs. Jones would have sold her 210 apples herself, she would
have received 52.50 euro.
Conclusion: Mrs. Jones loses 10.50 euro in this deal.