You compared two-digit numbers in Grade 1 (Comparing Two-Digit Numbers). Bigger numbers work the same way: start with the biggest place.
Why it works
One hundred is more than any number of tens and ones you can write with two digits: even 99 is 1 less than 100. So if one number has more hundreds, it is bigger, no matter what its other digits are. Only when the hundreds match do you look at the tens, and only when the tens match do you look at the ones.
Worked example: Different hundreds
Compare 312 and 299.
- Hundreds: 3 and 2. $3 > 2$.
- Stop here: 312 is bigger, even though 299 has bigger tens and ones.
Answer: $312 > 299$
Worked example: Same hundreds
Compare 532 and 528.
- Hundreds: 5 and 5, the same.
- Tens: 3 tens and 2 tens. $3 > 2$.
Answer: $532 > 528$
Worked example: Expanded form
Compare $400 + 9$ and 490.
- Write $400 + 9$ as a number: 409.
- The hundreds are the same. Tens: 0 tens and 9 tens.
- $409 < 490$.
Answer: $400 + 9 < 490$
Key idea
Compare the hundreds first, then the tens, then the ones. Write $>$ (greater than), $<$ (less than) or $=$ (equal). The open side of $>$ or $<$ faces the bigger number.
Common mistake
Picking the number with the biggest digits. 299 has two 9s, but 312 is bigger, because 3 hundreds beat 2 hundreds. Check: which number needs more hundred flats to build?
Grown-up tip: Compare page numbers or prices, and ask, “Which place did you look at first?”