Possibly, not all people know it can to make calculations inside Writer tables like in the Calc. But there are only 25 functions for use inside Writer tables, but Calc has over 400 functions.
To start use functions inside Writer tables you should left click into cell and then press key F2 or "=" on keyboard, or use "Formula" icon on Table toolbar. It shows a Formula bar like in the Calc.
There are Cell address field, Functions drop-down list, Cancel button, Apply button, Formula field on that bar.
Note, links to cells in Writer tables look as <A1> or <B3>. Cell ranges look as <A1:A10> or <A1:D12>.
After the Formula bar appeared you can select functions from drop-down list or can write a formula manually inside the Formula field after equal sign at once.
You can make calculates not only inside one Writer table. You can use values from many tables inside one Writer document. Use link to cell with table name like <Table2.A1>.
Attention! If you made in your formula a link to cell from another table and then changed that table's name, then you'll see an error in the cell like "** Expression is faulty **"! So, you should rename all your tables before you start create formulas inside these tables.
MS Word allows calculations in its native table too. But there are some differences between MS Word and LO Writer in that case.
First - difference between functions sets:
LibreOffice Writer table`s functions
MS Word table`s functions
|LESS THAN OR EQUAL||-|
|GREATER THAN OR EQUAL||-|
|COUNT (starting from 7.1)||
|ABS (starting from 7.1)||
|PRODUCT (starting from 7.1)
|SIGN (starting from 7.1)||
Second - in the Writer you type a formula into Formula bar like in the Calc, but in the MS Word you type a formula into the different dialog window.
Third - you can click on cells in the Writer tables when you create a formula, but in the MS Word you can't make it
Fourth - Writer can automatically recalculate result of formula when you change source values, but MS Word can't.
ps: if there is a formula inside a Writer table, then you'll never know about it wihout tooltip! Cell with formula looks like any another cell without formula in the table=(