Combining data validation and conditional formatting in Excel is a powerful way to improve data entry accuracy and provide visual cues to users. Here's how you can achieve this:

Scenario: Imagine you have a column (e.g., B) where users should only enter numbers between 1 and 10.

Steps:

1. Data Validation:
- Select the cell(s) where you want to restrict data entry (e.g., B2:B10).
- Go to the "Data" tab and click "Data Validation" in the "Data Tools" group.
- In the "Settings" tab, under "Allow," choose "Whole number" from the dropdown menu.
- In the "Minimum" box, enter "1."
- In the "Maximum" box, enter "10."
- Click "OK" to save the data validation rule.

2. Conditional Formatting:
- Select the same cell range (e.g., B2:B10) where you applied data validation.
- Go to the "Home" tab and click "Conditional Formatting" in the "Styles" group.
- Choose "New Rule..." from the dropdown menu.
- Select "Use a formula to determine which cells to format" under "Select a Rule Type."
- In the formatting rule box, enter the following formula: `=ISERROR(B2) OR (B2<1 OR B2>10)` (Replace B2 with your actual cell reference if needed).
Explanation:
- `ISERROR(B2)` checks if there's an error due to invalid data entry through data validation.
- `(B2<1 OR B2>10)` checks if the entered value is less than 1 or greater than 10.
- The formula combines these conditions using `OR`. If either condition is true, the formatting will be applied.
- Click the "Format" button to choose a formatting style (e.g., highlight with red fill).
- Click "OK" twice to close the windows and apply the conditional formatting rule.

Outcome:

- Users can only enter whole numbers between 1 and 10 due to data validation.
- If they enter an invalid value, the cell will be highlighted with the chosen format (red fill in this example), providing a clear visual cue that the data needs correction.

Additional Tips:

- You can customize the conditional formatting formula to suit your specific needs. For example, you can use different formulas to highlight different types of errors.
- You can combine data validation with other conditional formatting rules to create more complex data entry controls.

By combining these techniques, you can significantly improve data quality and user experience in your Excel spreadsheets.