Final answer:
When rounding a number, if the digit following the one you want to round is 5 or greater, you round the number up. If the digit is less than 5, you round the number down.
Step-by-step explanation:
When rounding a number, you look at the digit that follows the one you want to round. If that digit is 5 or greater, you round the number up. If it is less than 5, you round the number down. In this case, the number 0.12666666666 has a digit of 6 following it, so we round up to 0.13. Therefore, when rounded by 1, 0.12666666666 becomes 0.13.