Genesis 50:3

And they fulfilled forty days for him, for so are the days of embalming numbered; and Egypt mourned for him seventy days.

And forty days were fulfilled for him; for so are fulfilled the days of those which are embalmed: and the Egyptians mourned for him threescore and ten days.

Forty days were used for him, for that is how many days it takes to embalm. The Egyptians wept for Israel for seventy days.