Question

Suppose you subtract a 2-digit number from 200. Will you have to ungrounded hundreds or tens? Explain. Give an example.

Answer 1

You would have an underground number (aka negative number) because anything (greater than the minuend) that is subtracted from the minuend will get you an underground number. For example, 20 - 200 = -180.

Answer 2

You have to ungrounded tens.

Explanation:

If we subtract a 2-digit number from 200, this means that the number is between 10 and 99, this mean is a ten number, because it's based on tens. That's why we would have to unground tens, to subtract.

For example, let's subtract 30 from 200. So, basically we have to subtract 3 tens from 20 tens, which is 17 tens, or 170.

This method tend to help students to subtract in a easier way, when numbers are ten based.