Yes they can be. If they are formatted as text through the Format Cells option or put the single quote before it, they can still be treated as a number for calculation purposes. You can still use them in any kind of calculation, as long as there is no other actual characters in the cell, like letters. You can use a plus or minus symbol in the cells though.
You can use all Excel formats with numbers. If you use the text format, then the numbers are treated as text characters.
False
All numbers in Excel are actually decimal values (stored at the lowest level). The default is a best guess of how you typed it. Dates, numbers, etc. Remember - The format doesn't mean much of anything.. what's stored there remains the same.
The cell has been formatted to be in date format. You just need to format the cell to show numbers. If a number is formatted as a date, it will show an actual date.
Format | Format Cell | Number Tab | Number -- Click box in front of "Use 1000 Separator" >> In Excel this type of format is known as "accounting number format"
It is the "Format" that is applied to that cell's contents. Go to Excel Help and type "Format." There are lots of things including numbers which can be formatted. Numbers are in red if they are negative or greater or less than a limit.
You find scientific notation in Excel under the Format - Number menu.
There are many different formats for displaying numbers in an Excel cell including a general format, a currency format, a percentage format and an accounting format.
Format
Format.
Format.
general format