Answer: 10,000
Step-by-step explanation:
If you round to the nearest ten thousand, you round the number that makes it ten thousand in the first place.
Answer: From the right, you count 1 number, 0, then 2 numbers, 7, then 3 numbers, 8, then 4 numbers, and you get rid of those to make it 10,000.
Step-by-step explanation: Because 3, next to the 1 there rounds down, it makes 3,870 be rounded down overall.
