But he shall acknowledge the firstborn, the son of the hated, by giving him a double portion of all that is found with him; for he is the first of his strength, the right of the firstborn is his.
English: “A double portion” — a double portion as one (ordinary) share. Thus if there were five sons the firstborn takes one-third and the four ordinary sons take two-thirds.
On the daf / in context: The firstborn receives two shares out of the total number of shares equal to the number of sons plus one. He does not receive two-thirds of the entire estate regardless of the number of brothers.
Type of Learning
Derash clarifying the arithmetic of “pi shenayim.”
What Is Learned
The firstborn receives two ordinary shares; the estate is divided into as many shares as there are sons plus one extra share for the firstborn.