Final answer:
The upper bound for 1890s, rounded to the nearest 10, is 1900.
Step-by-step explanation:
When rounding a number to the nearest 10, you look at the digit in the ones place. If this digit is 5 or greater, you round up to the next 10. If the digit is less than 5, you round down to the current 10. In the case of 1890s, the digit in the ones place is 9, which is greater than 5. Therefore, when rounding to the nearest 10, the upper bound for 1890s would be 1900.