This particular problem is attributed to Alcuin. The wording does not give sufficient information to answer the question without making legal assumptions. Please share your assumptions with your solution.
A dying man left 960 shillings and a pregnant wife. He directed that if a boy was born, he should receive three-quarters of the whole and the child's mother should receive one-quarter. But if a daughter was born, she would receive seven-twelfths, and her mother five-twelfths. It happened however that twins were born - a boy and a girl. How much should the mother receive, how much the son, and how much the daughter?
There are obviously many assumptions that can be made to solve the dilemma. A reasonable assumption is to maintain the will's relative ratios of Son:Mom and Mom:Daughter in the final distribution. This gives the following 3 equations:
S + D + M = 960 ...........(1)
S = 3M ...........(2)
D = 7M/5 ...........(3)
Solving, we get: M = 1600/9 = 177 7/9 shillings
S = 4800/9 = 533 3/9 shillings
and D = 2249/9 = 248 8/9 shillings
How do we pay out a ninth of a shilling? That's another story!