Formatting of numbers

Q1) a b c d e f
555,000 225,000 155,000 £555k £225.5k 155k


in excel def will not add shows as count only
why?


Q2) why is the sum in cell E5 not working, the figures need to be shown in format they are in



also i need more practice when doing =sum,

such as =-(-sum what is the purpose of these minuses in some formulas came across =-(+sum

or

=-sum(a2:c2)-sum(d2:f2)/1000



i need to understand what these - and + are doing and are dong and how and when to write them to get the write answers

because the currency is cells a2:c2 is different to E2:G2

Q3) in the course he did cover how to changes units but cant remeber how at work got sheets with 3 formats of figures need to know how to do them ie;

55,000 in sheet 1

55k in sheet 2

5.5 in sheet 3



all for the same figure 55,000 but shown differently

can you advise how i can achieve this i think it was format cell custom and selecting one of the options but need to know what # means by adding or taking it away and why , makes a big diff to how figure is stated

thanks for your help