He died and left behind a wife, three sons and five daughters

Praise be to Allah.

If a man dies and leaves behind three sons, two of whom are from his wife and the third from another wife, and he leaves behind five daughters, then the estate is to be divided as follows: 

The wife gets one-eighth, because there are descendents who inherit. Allaah says (interpretation of the meaning): 

“but if you leave a child, they [wives] get an eighth of that which you leave after payment of legacies that you may have bequeathed or debts”

[al-Nisa’ 4:12]

The children, male and female, get the rest, with each male getting a share like that of two females, because Allaah says (interpretation of the meaning): 

“Allaah commands you as regards your children’s (inheritance): to the male, a portion equal to that of two females”

[al-Nisa’ 4:11].

In order to divide the estate (mathematically) among the heirs, it must be divided into 88 equal shares. The wife gets 11 shares, each son gets 14 shares and each daughter gets 7 shares. 

i.e., 

The wife’s share is: The estate x 11 ÷ 88. 

Each son’s share is: The estate x 14 ÷ 88. 

Each daughter’s share is: The estate x 7 ÷ 88. 

In this manner the share of each heir can be worked out precisely. 

And Allaah knows best.