excel 公式運算

You may use the Data Validation function to restrict the data entry on columns A to C.
The restriction of data entry relies on the total value on column E (upper limit of 40000), the error message can be defined in the “Error Alert” tab under “Data Validation…” for the alert:
1. Select the data input cell range A2:C20
2. Select menu Data --> (Data Tools Tab) Data Validation…
3. Select options under (i) Allow: ‘Decimal’ or ‘Whole number’; (ii) Data: ‘less than or equal to’; and put value under (iii) Maximum: ‘40000’)
4. Click the “Error Alert” tab, keep the ‘Style’ to be “Stop”, enter the desired ‘Title’ and ‘Error message’ (e.g. “Budget exceeded limit!” or 「超支」)
5. Select OK
Now you may test data entry and see if the restriction is effected. When the upper limit is exceeded during data entry, an error warning dialogue box will pop up to prohibit further data entry, so it seems not necessary to change cell colour to red.