Order of operation gives you 9 (which in this case is the correct answer), however, due to different math rules down in history you would have gotten the answer 1. Not anymore today, but a while back.
NEW METHOD:
6/2(2+1)
<=>
6/2(3)
<=>
6/2 * 3
<=>
3 * 3
<=>
9
OLD METHOD:
6/2(2+1)
<=>
6/2(3)
<=>...