Finding a Mistake in a Subtraction Problem
Jordan wants to solve the problem: 453-254 = ?
He begins by making an estimate.
450-250 = 200
Estimate:.
Then he uses expand-and-trade subtraction to find an exact answer, but his answer is not
close to his estimate. This is his work.

"Oops," says Jordan, "I didn't cross out 400 and write 300."
Explain why not changing 400 to 30 is a mistake.
Hint: Use what you know about place value in your answer.)