Answer:
5.1
Explanation:
The tenth's place is the first digit after the decimal. For rounding if the number behind your specific place is greater than or equal to 5, you round it up one number, if it is below 5 the number stays the same.
Example:
If I want to round 6.68 to the tenth's place since the 8 is greater than five, my 6 goes up one number and we get rid of the other numbers. Therefore it would be 6.7
If I want to round 6.64 to the tenth's place since the number is not greater than or equal to five, the number stays the same and we get rid of the others. Therefore it would be 6.6
In your case of 5.1249, we only look at the number after the tenth's place to check if it is greater than or equal to five, which it is not, which is why we do not round up, giving us 5.1.