There are a number of verses that tell Muslims how to manage inheritance: 2:180, 2:233, 2:240, 4:12, 4:13, 4:176 and 5:106. However, the verses that go through the detailed mathematics are 4:12, 4:13, and 4:176:
YUSUFALI: Allah (thus) directs you as regards your Children's (Inheritance): to the male, a portion equal to that of two females: if only daughters, two or more, their share is two-thirds of the inheritance; if only one, her share is a half. For parents, a sixth share of the inheritance to each, if the deceased left children; if no children, and the parents are the (only) heirs, the mother has a third; if the deceased Left brothers (or sisters) the mother has a sixth. (The distribution in all cases ('s) after the payment of legacies and debts. Ye know not whether your parents or your children are nearest to you in benefit. These are settled portions ordained by Allah; and Allah is All-knowing, Al-wise.
PICKTHAL: Allah chargeth you concerning (the provision for) your children: to the male the equivalent of the portion of two females, and if there be women more than two, then theirs is two-thirds of the inheritance, and if there be one (only) then the half. And to each of his parents a sixth of the inheritance, if he have a son; and if he have no son and his parents are his heirs, then to his mother appertaineth the third; and if he have brethren, then to his mother appertaineth the sixth, after any legacy he may have bequeathed, or debt (hath been paid). Your parents and your children: Ye know not which of them is nearer unto you in usefulness. It is an injunction from Allah. Lo! Allah is Knower, Wise.
SHAKIR: Allah enjoins you concerning your children: The male shall have the equal of the portion of two females; then if they are more than two females, they shall have two-thirds of what the deceased has left, and if there is one, she shall have the half; and as for his parents, each of them shall have the sixth of what he has left if he has a child, but if he has no child and (only) his two parents inherit him, then his mother shall have the third; but if he has brothers, then his mother shall have the sixth after (the payment of) a bequest he may have bequeathed or a debt; your parents and your children, you know not which of them is the nearer to you in usefulness; this is an ordinance from Allah: Surely Allah is Knowing, Wise.
YUSUFALI: In what your wives leave, your share is a half, if they leave no child; but if they leave a child, ye get a fourth; after payment of legacies and debts. In what ye leave, their share is a fourth, if ye leave no child; but if ye leave a child, they get an eighth; after payment of legacies and debts. If the man or woman whose inheritance is in question, has left neither ascendants nor descendants, but has left a brother or a sister, each one of the two gets a sixth; but if more than two, they share in a third; after payment of legacies and debts; so that no loss is caused (to any one). Thus is it ordained by Allah; and Allah is All-knowing, Most Forbearing.
PICKTHAL: And unto you belongeth a half of that which your wives leave, if they have no child; but if they have a child then unto you the fourth of that which they leave, after any legacy they may have bequeathed, or debt (they may have contracted, hath been paid). And unto them belongeth the fourth of that which ye leave if ye have no child, but if ye have a child then the eighth of that which ye leave, after any legacy ye may have bequeathed, or debt (ye may have contracted, hath been paid). And if a man or a woman have a distant heir (having left neither parent nor child), and he (or she) have a brother or a sister (only on the mother's side) then to each of them twain (the brother and the sister) the sixth, and if they be more than two, then they shall be sharers in the third, after any legacy that may have been bequeathed or debt (contracted) not injuring (the heirs by willing away more than a third of the heritage) hath been paid. A commandment from Allah. Allah is Knower, Indulgent.
SHAKIR: And you shall have half of what your wives leave if they have no child, but if they have a child, then you shall have a fourth of what they leave after (payment of) any bequest they may have bequeathed or a debt; and they shall have the fourth of what you leave if you have no child, but if you have a child then they shall have the eighth of what you leave after (payment of) a bequest you may have bequeathed or a debt; and if a man or a woman leaves property to be inherited by neither parents nor offspring, and he (or she) has a brother or a sister, then each of them two shall have the sixth, but if they are more than that, they shall be sharers in the third after (payment of) any bequest that may have been bequeathed or a debt that does not harm (others); this is an ordinance from Allah: and Allah is Knowing, Forbearing.
YUSUFALI: They ask thee for a legal decision. Say: Allah directs (thus) about those who leave no descendants or ascendants as heirs. If it is a man that dies, leaving a sister but no child, she shall have half the inheritance: If (such a deceased was) a woman, who left no child, Her brother takes her inheritance: If there are two sisters, they shall have two-thirds of the inheritance (between them): if there are brothers and sisters, (they share), the male having twice the share of the female. Thus doth Allah make clear to you (His law), lest ye err. And Allah hath knowledge of all things.
PICKTHAL: They ask thee for a pronouncement. Say: Allah hath pronounced for you concerning distant kindred. If a man die childless and he have a sister, hers is half the heritage, and he would have inherited from her had she died childless. And if there be two sisters, then theirs are two-thirds of the heritage, and if they be brethren, men and women, unto the male is the equivalent of the share of two females. Allah expoundeth unto you, so that ye err not. Allah is Knower of all things.
SHAKIR: They ask you for a decision of the law. Say: Allah gives you a decision concerning the person who has neither parents nor offspring; if a man dies (and) he has no son and he has a sister, she shall have half of what he leaves, and he shall be her heir she has no son; but if there be two (sisters), they shall have two-thirds of what he leaves; and if there are brethren, men and women, then the male shall have the like of the portion of two females; Allah makes clear to you, lest you err; and Allah knows all things.
"Allah makes clear to you, lest you err; and Allah knows all things."
OK, so let's all remember that Allah makes it all clear to you because he knows all things. So, if we notice that three Muslims give three different answers (and they will), then there must be another contradiction...simply that Allah is not clear after all.
The Math and the mistake
So let's go back to the original question:
Now, calculate how to split the inheritance for a man how dies and leaves behind: 3 daughters, 2 parents and two wives.
3 daughters: x%
2 parents: y%
2 wives: z%
Here's the answer with the supporting quotes.
3 daughters: 2/3
4:11 : "if only daughters, 2 or more, their share is 2/3 of the inheritance"
2 parents: 1/6+1/6=1/3
4:11 : "For parents, a 1/6 share of the inheritance to each, if the deceased left children"
2 wives: 1/8
4:12 : "in what ye leave, their share is 1/4, if ye leave no child; but if ye leave a child, they get an 1/8"
Now, let's add up the inheritance divisions up:
2/3+1/3+1/8 = 9/8 >1
Mistake! Allah can't do math. How can you possibly give away more inheritance than you have? Now, I pointed out just one math mistake, but there are many. In the next set of posts I will go through the typical, albeit false, objections to Islamic mathematics.