Gustav is using front-end estimation. In estimating seventy-two point nine three minus thirty-two point zero seven, Gustav follows the steps below. Where did he go wrong?

Question

Step 1: seventy-two minus thirty-two equals forty
Step 2: zero point nine three minus zero point zero seven is approximately equal to one
Step 3:forty minus one equals thirty-nine
Step 4: seventy-two point nine three minus thirty-two point zero seven is approximately equal to thirty-nine

Answer 1

"Step 3:forty minus one equals thirty-nine "

We add the integer and decimal portions, not subtract.