Hello Houjun,

Thanks for using the Online Course Discussion Forum!

Remember that any 3 digit number can be broken down into hundreds, tens, and ones. For example: 987 = 900 + 80 + 7 = 9*100 + 8*10 +7*1. Therefore, 987 has 9 hundreds, 8 tens, and 7 ones.

For the case of 987, this number is an example of a situation where there are 8 tens, and 1 less ones than tens (8 - 1 = 7 ones).

I hope this clarifies the question. Please let me know if you need any help!

Best,
Wilson